Physical! Sci .Lib.

TN 24 C3 A3 NO. 201

PHYSICAL S«K AN EXPLANATORY TEXT SI TO ACCOMPANY THE 1:750,000 SCALE FAULT AND GEOLOGIC MAPS OF CALIFORNIA

PURPOSE AND USE EVOLUTION OF FAULT AND GEOLOGIC MAPS FAULTS AND EARTHQUAKES MAJOR STRUCTURAL BLOCKS OF CALIFORNIA FAULT PATTERNS VOLCANOES THERMAL SPRINGS AND WELLS INDEXES TO: Faults Hot Springs Formations Source Data

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BULLETIN 201

AN EXPLANATORY TEXT TO ACCOMPANY THE 1:750,000 SCALE FAULT AND GEOLOGIC MAPS OF CALIFORNIA

By

Charles W. Jennings Geologist

1985

L^ CALIFORNIA DEPARTMENT OF CONSERVATION ^^'"'M^ DIVISION OF MINES AND GEOLOGY 1416 NINTH STREET, ROOM 1341 SACRAMENTO, CA 95814

CONTENTS

Page

Preface vii Abstract ix

Introduction 1

Purpose and uses 1 Value of map compilations 2 Base Mop 2 Source data 2 Acknowledgments 3

Part I Fault Map of California

Introduction 7 Recognition of faulting as cause of eartliquakes 7 Evolution of fault maps of California 7 First fault map of the state— 1908 7 Second fault map of California— 1922 - 9 Faults sfiown on Geologic Map of California— 1938 10 Combined Wood and Jenkins fault map of tfie southern half of the state— 1947 11 Earthquake Epicenter and Fault Map of California— 1964 12 Earthquake Epicenter Mop of California— 1978 12 Small-scale fault maps of California 12 Preliminary Fault and Geologic Map of California— 1973 14 Fault Map of California— 1975 edition 14 Depiction of faults 15 Fault classification 15 Fault definitions 15 Historic faults, earthquakes, and creep 16 Earthquakes with surface rupture 16 Recorded fault creep 18 Displaced survey lines 23 Seismicity 23 Quaternary faults 24 Identification 24 Problems 24 Plio-Pleistocene boundary controversy 26 Major Quaternary faults 26 Philosophy of conservatism 26 Pre-Quoternory faults 27 Accuracy of fault locations 27 Offshore structure 28 Coast Range thrust 28 Circular fault structures 28

Future changes in fault depiction 29 Fault patterns 30 Structural provinces 30 Predominant fault trends defining structural provinces 31 Major structural blocks with predominantly northwest faults 31 Coast Ranges block 31 Peninsular Ranges block 31 Major structural block having predominantly east-trending faults 31 Transverse Ranges block 31 Santa Ynez and Son Gabriel sub-blocks 31 Banning sub-block 31 San Bernardino sub-block 31 Pinto Mountains sub-block 31 Major structural blocks charocterized by northeast-trending fault boundaries 32 Mojove block 32 Tehachapi block 32

iii Page

Major structural blockj charocterized by north-trending faults 32 Kern Canyon block 32 Ponomint and Death Valley blocks 32 Worner block 33 East Sierra block 33 Cascade block 33 Gordo block 33 Major structural blocks characterized by other types of faults 33 Sonoran Desert block 33 Sierra Nevada block 33 Klamath block 33 Modoc block 33 Coast Ranges sub-blocks 33 Santo Lucia and Gobilan sub-blocks 33 Son Francisco ond Berkeley sub-blocks 34 Diablo and Great Valley sub-blocks 34 Stonyford sub-block 34 Peninsular Ranges sub-blocks 34 San Clemente and Cotalina sub-blocks 34 Polos Verdes and Inglewood-Son Diego sub-blocks 34 Santa Ana, Riverside, and Son Jacinto sub-blocks 34 Sub-blocks within the Modoc block 34 Summary 34 Fault couples 35 En echelon faults 35 Regularity of fault spacing 35 Summary on fault geometry 39 Faulting and patterns of seismicity 39 Relationship of epicenters to faults 39 Relationship of surface rupture to earthquake magnitude 41 Faults with recurring earthquake activity 41 Patterns of seismicity 42 Cautions in use of Fault Map of California for land-use planning 42 Depiction of volcanoes 43 Distribution and age 43 Relation of volcanoes to faults 44 Volcanic hazards 44 Depiction of thermal springs and wells 45 Temperoture 45 Mode of occurrence of hot springs 45 Distribution of hot springs 45

Part II Geologic Map of California

Introduction 51 History of geologic mops of California 51 The first attempts 51 Preliminary Minerological and Geological Map of the State of California— 1891 51 Geological Mop of the State of Colifornia— 1916 51 Geological Mop of California— 1938 52 Geologic Atlos of California— 1958-1969 52 Two smoll-scole geologic maps of California (1966 and 1968) 54 Geologic Map of California— 1977 54 History of the project 54 Uses of the geologic map 55 Objectives and contents 56 Representation of faults 56 Representation of contacts 56 Compilation method 56 Classification of rock units and special problems 58 Colors, patterns, symbols of rock units, ond mop appearance 61 Geologic time scale 66 Volcanoes 66 Botholiths ond plutons 66 Offshore geology 68

References cited in Parts I ond II 69

iv Part III Appendices

Page

APPENDIX A: INDEX TO FAULT NAMES SHOWN ON THE FAULT MAP OF CALIFORNIA, 1975 EDITION

Named faults shown 77 Procedure for naming faults 77 Index to fault names 78 Supplemental index to fault names 80

APPENDIX B: TABULATED LIST OF THERMAL SPRINGS AND WELLS

Data used and acknowledgments 81 Locating thermal springs and wells 81

Tabulated list of thermal springs and wells 81

References cited in Appendix B 1 17

APPENDIX C: INDEX TO THE GEOLOGIC FORMATIONS GROUPED WITHIN EACH UNIT PORTRAYED ON THE GEOLOGIC MAP OF CALIFORNIA, 1977 EDITION

Explanation 1 19 Index 120

APPENDIX D: SOURCE DATA INDEX

How to use this index 125 Other references 125 Indexes to published geologic maps 125 Indexes to theses 125 Explanation of maps 127 Bibliography (by atlas sheet) 128

LIST OF ILLUSTRATIONS

Figures

Figure 1. Increase of published geologic map data for California 2 Figure 2. Theses on California geology 1892-1976 (exclusive of topical and brood regional studies) 3 Figure 3. Bruce Clark's 1930 map of California showing "principal known primary faults" 13 Figure 4. Mop of California and adjacent terrone showing major Quaternary faults and identifying historic fault breaks, occurrences of fault creep, and triggered creep 19 Figure 5. Mop showing small-magnitude earthquake epicenters reported during 1975 25 Figure 6. Generalized mop of the Long Volley-Mono Craters area showing location of faults 29 Figure 7. Numerous short NW and NE conjugate faults characteristic of the Panomint and Death Valley blocks 32

Figure 8. Diagonal faults formed between two major strike-slip faults, the Son Andreas and the Rodgers Creek-Heoldsburg faults ... 36 Figure 9. Diagonal faults formed between the strike-slip Son Andreas and Son Gabriel faults 37 Figure 10. Diagonal folds formed between the San Andreas and Rinconada faults in thin sedimentary cover overlying granitic basement rocks 38 Figure 11. Fracture zones illustrated by Menard (1955) 40 Figure 12. Part of a tectonic mop of the world (Condie, 1976) including the same area illustrated by Menard 40 Figure 13. Alignment of Tertiary volcanic plugs near San Luis Obispo along a line of weakness presumed to be on ancient fault 44 Figure 14. Relief Mop of California showing geomorphic provinces 48 Figure 15. Geologic Legend (generalized description of rock types) 62-63 Figure 16. State index map showing the boundaries of the individual Geologic Atlas sheets and the source data index mops in Appendix D 126 Page

Tables

Table 1. Summory of published foull mops of Colifornia 14 Table 2. Comporison of various commonly used fault definitions 17

Table 3. Evidence used for determining fault history 17 Table 4. Port A. Historic surface faulting associated v/ith earthquakes in California 20

Port B. Historic surface faulting associated with earthquakes in Nevado ond Bajo California 22 Port C. California faults displaying fault-creep slippage not associated with earthquakes 22 Part D. Triggered creep along faults associated with earthquakes in California 23

Table 5. California seismic record for 75 years 41

Table 6. Observed volcanic events in California 44 Table 7. Springs neor boiling point temperature 46 Table 8. State geologic mops of California 52 Table 9. Geologic otlos of California (1 -.250,000 scale) 53 Table 10. Derived legend for 1:750,000 scale Geologic Mop of California 59-60 Table 11. Comparison of "American" and "International" mop colors for sedimentary rocks 64 Table 12. Comparison of "American" and "International" map colors for plutonic and volcanic rocks 64 Table 13. Patterns used on Geologic Mop of Colifornio 65 Table 14. Geologic time scale 67 Table 15. Botholifh, plutons, and stocks identified on the 1977 Geologic Mop of California 68

Plates (in pocket)

Plate lA. Faults shown on the first fault mop of California. From Mop No. 1 of the State Earthquake Investigation Commission report on the

California earthquake of April 18,1906 (Lowson and others, 1908) . Fault names shown in quotation marks ore from the text of 1908 report; other fault names were added from current usage.

Plate 1 B. H. O. Wood's abridged version of Lawson's 1908 fault map of California, showing faults and "lines" tentative!/ considered by Wood to be generatrices of earthquakes.

Plate IC. Faults shown on the Fault Map of California compiled by B. Willis ond H. O. Wood and published by the Seismologlcal Society of America in 1922 at o scale of 1:506,880.

Plate ID. Faults shown on the Geologic Mop of California published in 1938 at 1:500,000 scole. This reduced version, showing faults only, includes all those faults shown on the larger scale mop. Faults were not shown by name on the original mop, but have been identified on this plate.

Plate IE. Foult mop of southern California (here slightly generalized) compiled by H. O. Wood. Faults were taken largely from the 1922 Fault Mop of Californio and the 1938 Geologic Mop of California.

Plate 2A. Structural provinces of California determined by the prominent fault patterns and characteristics of the faults they contain or bound.

Plate 2B. Parallelism between major Quaternary faults and regularity of fault spacing.

Plate 2C. Relationship of earthquake epicenters to faults in California. Note the close relationship of earthquakes of magnitude 6 and greater to the major Quaternary faults.

Plate 2D. Eorthquoke epicenters of mognitude 4 to 4.9, showing more scatter than for the larger earthquakes, but also suggesting certain areas of low historic seismicity.

VI PREFACE

This bulletin was prepared after the GEOLOGIC MAP OF CALIFORNIA was published in 1977. The parts dealing with hot springs and wells, and with source data, now included in the appendices to this bulletin, were prepared in draft form in conjunction with the FAULT MAP OF CALIFORNIA published in 1975. Most of the text was written in 1978 and a first draft was reviewed at that time. After several delays the manuscript was approved for publication in 1981.

The data in Appendix B, Tabulated List of Thermal Springs and Wells have been incorporated in the U.S. Geological Survey GEOTHERM data bank and later the California Division of Mines and Geology, Geologic Data Mop No. 4, GEOTHERMAL RESOURCES OF CALIFORNIA. It is included in this bulletin as documentation for the locations of thermal springs and wells shown on the FAULT MAP OF CALIFORNIA, WITH LOCATIONS OF VOLCANOES, THERMAL SPRINGS AND THERMAL WELLS,

Geologic Data Map No. 1.

is still to the The Source Data Index (Appendix D) , although somewhat outdated, the best guide most useful and available areal geologic mapping in California to approximately 1972, and its annotations indicate the sources used to classify the recency of activity of faults in California. The Source Data Index also contains some data to 1975.

This bulletin reviews the history and development of geologic and fault maps of California. The author has taken this opportunity to articulate various ideas and speculations pertaining to the geology and structure of California that have occurred to him over the years he has spent compiling maps published by the California Division of Mines and Geology.

VII

ABSTRACT

The latest in a series of State Geologic Maps of California was published in 1977, and a Fault Map of California was published in 1975. Bulletin 201 attempts to put these maps in historical perspective by describing in chronological order the earlier state maps of both these types. The bulletin explains various uses for these maps and also discusses precautions against their misuse.

This volume is divided into three parts. The first deals with the Fault Map of California. The evolution of fault maps of California is described beginning with the first fault map of the state (published in 1908), and ending with a detailed description of the 1975 Fault Map of California.

Emphasis is placed on historic and Quaternary faults and the criteria used to classify them. Fault patterns recognized in California are discussed, and structural provinces of the state, as defined by predominant fault trends, are proposed. The hmitations in the use of the Fault Map of California for land-use planning are reviewed. Finally, a discussion of the volcanoes and thermal springs and wells that are plotted on the Fault Map concludes the first part of Bulletin 201. The second part of the bulletin, pertains to State geologic maps of California. A brief historical account of early geologic maps of the state is followed by a discussion of the 1977 edition. The objectives and contents of the map are described, and considerable explanation is given to the compilation method and the physical apjjearance of the map, including a discussion of the choice of colors, patterns, and symbols. A brief explanation of batholiths and other plutons, as well as the offshore geology, follows. The third part of the bulletin consists of reference data organized in four appendices. Appendix A is an index to the 272 fault names shown on the Fault Map of Cahfomia. In addition, a procedure for the naming of faults that would avoid repetition and confusion is suggested. Appendix B consists of a tabulated hst of 584 thermal springs and wells, organized by 1° x 2° State Map Sheet units. This list contains location and temperature data, and pertinent refer- ences. For the thermal wells, total depth and year drilled are also given. The location of each thermal spring and well is shown on the index maps to the source data in Appendix D.

Appendix C is an index to the over 1,000 geologic formations grouped within the units portrayed on the 1977 Geologic Map of California. Lastly, Appendix D is an extensive index to the source data used to compile the Geologic Map and for classifying the faults on the Fault Map. This index is keyed to 28 maps showing in detail the area covered by the references listed in the bibliographies. Bulletin 201 consists of 197 pages, including 16 figures, 15 tables, and two plates. The Bulletin was designed to accompany the Fault Map of California (1975) and Geologic Map of California (1977), and hopefully will enhance the usefulness of these maps by providing additional explana- tion and background data.

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AN EXPLANATORY TEXT TO ACCOMPANY THE 1:750,000 SCALE FAULT AND GEOLOGIC MAPS OF CALIFORNIA

BY CHARLES W. JENNINGS

INTRODUCTION The Geologic Map of California and the Fault Map of Califor- nia are syntheses of the available information on the geology and The Fault Map of California (1975), the Geologic Map of structure of California. An attempt was made to summarize and California (1977), and this bulletin culminate nearly ten years incorporate some of the currently accepted conclusions regard- of extensive research. To a degree these maps represent the ing the geologic evolution of California, for example, depiction "state-of-the-art" in California regional geology. They supersede of the Coast Range thrust fault as the upper boundary of a late the Prehminary Fault and Geologic Map of California on the Mesozoic subduction zone; however, little attempt was made to same 1:750,000 scale, published by the California Division of devise a uniform structural interpretation of the entire state.

Mines and Geology in 1973. Uniformity is certainly desirable; however, it was believed that

The Geologic Map of California presents an overview of the to achieve it on a map of a state as large and complex as Califor- geology and structure of the state with sufficient detail to be nia would be a difficult and time-consuming task and might even useful for many purposes. It should fill the need for a modem prove to be of dubious value. It was decided, therefore, to con- geologic wall map showing the distribution of the major rock centrate more intently on the basic data, namely the distribution types and the major structural elements of the state. The Fault of the various rock units, and generally to use the structural Map of California, on the other hand, emphasizes fault activity interpretations shown by the authors of the source data. in the state and differentiates faults according to time of activity. In synthesizing data from individual maps, an attempt was The fault map also shows the locations of the numerous recent made to follow the field geologist's interpretation as closely as volcanoes in California and the locations of all known thermal possible, but in order to harmonize one map with another, it was springs and wells. often necessary to be arbitrary in the selection of what is most This bulletin was prepared to accompany the Fault Map and significant. No two compilers will make identical decisions; the Geologic Map and is intended to enhance their usefulness by however, at the onset of this project, guidelines were established providing additional explanation. This report also describes the and followed by all those who assisted in the compilation. In the historical antecedents of these two maps, the latest in a sequence final map-synthesis, the writer tried to view the state as a whole of state geologic maps that was started in 1891. No attempt has and tried to give the compilation a certain balanced judgment. been made to write a comprehensive "Geology of California" Thus, in the resulting maps, the depiction of faults, especially so much is now known and the problems are so complex that recent faults, was considered more important than the portrayal California geology, for most intents and purposes, has become of rock types. In congested areas, faults may have sometimes the field of specialists. Nor has the writer attempted to summa- been exaggerated by connecting several segments, or by general- rize or generalize the basic facts of Cahfomia's geologic history izing the local geology. because at least two effective overviews have been published in recent years; G.B. Oakeshott's "California's Changing Land- scapes" (1971 and 1978), and Norris and Webb's "Geology of Purpose and Uses California" (1976). Readers are referred to these texts, as start- ers, if they are unfamiliar with the geologic setting in California. The primary purpose in preparing the Geologic Map of Cali- For more advanced considerations of California geology, the fornia was to show clearly the regional relationships of rock and recent literature abounds with outstanding papers. Some of the time-rock units in California, and of the Fault map of California, most instructive are the outgrowth of symposia on various top- to depict the faults as to their recency of movement. The maps ics, or field trip guides to specific areas within the state. To list summarize up-to-date geologic information on California for use these would require much space; however, the reader is referred in applied and theoretical geology. to the "References Cited in Parts I and 11" on pages 69-74 These are multipurpose maps. The Geologic Map portrays the wherem many useful papers are included. geologic setting of mineral deposits of California and can be used

Bulletin 201 consists of two main parts and four extensive in planning mineral resources investigations. It is helpful in mak- appendices. Part I is a detailed explanation of the Fault Map of ing regional land-use plans, soil surveys, and in locating and California and Part II is a discussion of the Geologic Map of planning large-scale civil engineering projects such as roads,

California. Part III contains four appendices: ( 1 ) an index to the dams, tunnels, and canals. The Fault Map is an inventory of faults shown on the 1975 edition of the Fault Map, (2) a tabulat- faults in the state and can be useful in preliminary earthquake ed listing of data for the thermal springs and wells depicted on hazard evaluations. A preliminary version of this map was pub- the Fault Map, (3) an index to the geologic formations grouped lished to aid local governments in preparation of seismic safety within each of the units shown on the Geologic Map of Califor- elements required by California law as part of the general plans nia, and (4) a detailed bibliography keyed to 27 index maps (or master plan) for cities and counties. The Fault Map is also identifying all of the source data used to compile the Geologic useful as a guide to Quaternary and recent volcanism and thus Map and Fault Map. is useful in consideration of possible volcanic hazards. Lastly, the DIVISION OF MINES AND GEOLOGY BULL. 201

locations of thermal springs and wells shown on the Fault Map in the San Francisco Bay Region Environment and Resources are indications of abnormally high temperature gradients and I'lannmg Study was invaluable in the revision of several Bay area are useful in the exploration and development of geothernial sheets. power. The Geologic Map of California and the Fault Map of Unlike the extensive mapping done by the staff of the Division California are also useful in classrooms for those teaching and of Mines and Geology for the preparation of the State Geologic studying geology, seismology, and geophysics, a.s well as related Atlas, most of the Division maps used in the 1:750,000 scale fields such as geography, oceanography, ecology, and soils. compilation were taken from projects such as the urban mapping cooperative projects with cities and counties and from the com- 7 Value of Map Compilations pletion of 15-minute or '/;-niinute quadrangle projects. The preparation of a totally revised 1:250,000 scale Death Valley sheet (Streitz and Stinson, 1977) was especially useful, and in- A compilation is no better than the data sources from which deed, was done in part to aid the 1:750,000 scale compilation. it is compiled, which usually vary from detailed to general maps. Work done by the Division specifically for the 1:750,000 compi- A compilation, however, can go beyond the sco[)e of the source lation included extensive photo-interpretation of Quaternary maps and reveal broader relationships, by virtue of the capability faults in northeastern California and field evaluations of selected of synthesizing individual areas and thereby revealing important faults to determine their extent or recency of movement. regional trends. A careful synthesis thus reveals new concepts, Preparation of the 1:750,000 scale map began in 1969, and which because of their magnitude, may be more important than revisions were added to keep the work sheets current until about the details. 1972. An extensive review of the product was then undertaken with the help of many geologists both inside and outside the Base Map Division of Mines and Geology. As a result, numerous changes and additions were made to the compilation. After 1974, while The base map used on the Fault Map of California and the the maps were being drafted for publication, no attempt was Geologic Map of California is a reduction of the two-sheet made to keep the compilation current, because of lack of time 1:500,000 scale Map of California published in 1970 by the U.S. and the difficulties of making piecemeal revisions of areas which Geological Survey. These two sheets were reduced to 1:750,000 had already been drafted. However, some later data, especially scale and joined to make a single map 4 '/: by 5 feet. The use of newly recognized faults, or data affecting the fault classification, a single large-size sheet instead of two separate sheets eliminated were incorporated. The offshore area was the largest single area problems in registration and matching of colors from sheet to thus affected, because of the vast amount of new data released sheet and, most important of all, allowed the faults, geologic by the U.S. Geological Survey. All reference data used in the formations, and structures to be displayed with uninterrupted compilation are indexed by atlas sheets, and shown m Appendix continuity. D. The base map indicates county boundaries in green; cities and towns, highways and roads, railroads, and the township-and- range boundaries in black; and rivers, streams, and other water features, including ocean depth curves at 100 fathom intervals, in blue. Contours, at 500-foot intervals with 100-foot supplemen- tary intervals, are shown in brown on the Fault Map and are available on the Geologic Map (part of the first printing of the

Geologic Map was without contours). The base map is a Lam- bert conformal conic projection, based on standard parallels 33° and 45°. The highways shown are correct to 1969. ^-1270 — GEOLOGIC MAPS Source Data

In a state as large and geologically complex as California, the quality and accuracy of the geologic mapping varies. In general, the latest information available was used. The 1:250,000 scale Geologic Atlas of California was the principal source, but exten- sive revisions were made and nearly 900 new references were added, approximately 30 percent of which were from unpub- lished sources. The continual progress and rate of growth in preparation of published and unpublished geologic maps in California are shown in Figures 1 and 2. Among the unpublished data, besides geologic theses and dis- 278 GEOLOGIC MAPS sertations, some company and consultant reports arc included and unpublished maps by geologists of the California Division of Mines and Geology and other Stale and Federal agencies, especially the California Department of Water Resources, and 105 217 383 670 the U.S. Geological Survey. Extensive reconnaissance maps of 37 27 56 45 parts of the northern Coast Ranges, which were made by the 1850 60 70 80 90 1900 10 20 30 40 50 I960 1970 Department of Water Resources in connection with proposed PUBLICATION YEAR dams and tunnel routes, were very useful in revising the Ukiah

Sheet area, and the extensive work by the U.S. Geological Survey Figure 1. Increase of published geologic mop doto for Colifornio. 1985 TEXT TO ACCOMPANY THE FAULT AND GEOLOGIC MAPS OF CALIFORNIA

60

55

50

45

V) XUJ H- 35 Oli. ir 30 CD i25H

20

10

p. niil XL Jl in £1 1892 95 1900 05 10 20 25 30 35 40 45 50 55 60 65 70 1975 YEAR

Figure 2. Theses on California geology 1892-1976 (exclusive of topical and broad regional studies).

Acknowledgments sistance in the location of historically active faults, and his un- published catalog of "Earthquakes with Surface Faulting or The Fault Map of California and the Geologic Map of Califor- Ground Breaks and Creep Events" was particularly valuable. R. nia are based on the work over many years by a vast array of Streitz and M.C. Stinson substantially improved the representa- geologists and institutions. In a way, these two maps represent tion of the geology in the Death Valley Sheet area by the prepara- about 150 years of geologic exploration and mapping since Lieu- tion of a new compilation of this sheet (Streitz and Stinson, tenant Edward Belcher first surveyed the "Port of San Fran- 1977). Robert Switzer assisted in the interpretation of some of cisco," which became in 1839 the first published geologic map the latest geologic data used in updating the compilations and of any part of California. Acknowledgment therefore goes to all also in making numerous corrections immediately prior to sub- the geologists down the years who have mapped in California, mittal of the maps to the printer. The painstaking task of color- for only by drawing on this collective body of knowledge have ing the preliminary compilation, photographic prints of which we arrived at our present level of understanding of the state's were used in the reviewing process, was done by my daughter, rocks and structure. Marcia Jennings.

Within the Division of Mines and Geology, the writer is espe- The compilations benefited greatly by the comments and new cially grateful to R.G. Strand and T.H. Rogers for their assist- data generously provided during careful review of this map by ance in compiling and revising the 1:250,000 scale work sheets members of numerous federal and state agencies, as well as during the first stages in the preparation of the compilation. independent geologists familiar with California geology. At the

M.C. Stinson in the later stages helped revise the depiction of risk of appearing partial, I would like to mention the following selected Quaternary and historic faults, and J.L. Burnett pre- geologists who made particularly constructive suggestions or pared a photogeologic interpretation of Quaternary faults for the contributed new data covering large areas of the state; E.H. northeastern part of the state. J.E. Kahle provided valuable as- Bailey, E.E. Brabb, T.W. Dibblee, Jr., P.E. Hotz. W P. Irwin, DIVISION OF MINES AND GEOLOGY BULL. 201

R.D. Nason. H.C. Wagner, CM Wentwonh, and J.I Ziony, all The maps were printed by the Williams and Heintz Map of the U.S. Geological Survey; Professors C.R. Allen, California Corporation of Washington D.C., under the masterful supervi- Institute of Technology; J.C. Crowell, University of California, sion of William Heintz. Mr. Heintz's keen interest, cooperation, Santa Barbara; C.A. Hall. University of California, Los Angeles; and patience were demonstrated time after time while we experi- B.M. Page, Stanford University; C. Wahrhaftig, University of mented with difTerent colors, shades, patterns, and formats. California, Berkeley; and ML. Hill and A.O. Woodford, Po- In the preparation of this manuscnpt, two of the four appen- mona College, Claremont, California. To all these geologists and dices— the Tabulated List of Thermal Springs and Thermal many other unnamed contributors, the State is especially grate- Wells and the Source Data Index—could not have been possible ful. without the extensive help of John Sackett, Duane McClure, Of all the individual contributors to the geologic mapping of Melvin Stinson, and Robert Switzer, who plotted most of the California, surely Thomas W. Dibblee, Jr. warrants special rec- thermal springs and wells; David Peterson, who assisted in the ognition and appreciation. A vertiable one-man geological sur- preparation of the source data index; and Robert Switzer, who vey, he mapped and published more than eighty-four 15-minute drafted most of the plates. The initial manuscript was edited by and thirty-five 7 ' .-minute quadrangles. In addition, Mr. Dibblee Virginia McDowell. Dorothy Hamilton carefully and cheerfully has numerous geologic quadrangles that he has mapped but not typed and proof-read this manuscript, including all the extensive published. listings, and all the revisions. The immense task of scribing and preparing the plates for Special thanks are due B.W. Troxel, R.D. Nason, J.W. Wil- publication was e.xpertly done by R.R. Moar, R.T. Boylan, and liams, G.B. Oakeshott, D.L. Wagner, S.J. Rice, R.G. Strand, and R.A. Switzer of the Division. The Fault Map of California and C.R. Real, who read all or parts of the manuscript and generous- The Geologic Map of California could not have become a reality ly aided with constructive criticism. without the ready help of Merl Smith, Publications Supervisor To all those mentioned above, and all the unnamed individuals of the California Division of Mines and Geology. His sage advice who over the years contributed or encouraged the preparation of in lithographic matters and his assistance in obtaining the type these two maps and this bulletin, I wish to express deepest thanks of map we desired are especially recognized. and appreciation. PART I FAULT MAP OF CALIFORNIA

He looketh on the earth, and it trembleth:

He toucheth the hills, and they smoke.

-Psalm 104 Verse 32

FAULT MAP OF CALIFORNIA

INTRODUCTION elastic rebound theory by 24 years (but, without of course, the benefit of Reid's rigorous analysis of accurate triangulation sur- The 1975 Fault Map of California depicts the most recent veys across the San Andreas fault): knowledge on the distribution and nature of faults in California. is slips It also indicates as factually as possible the activity of the faults. The ground broken and either up, down, or side- Indications of the degree of activity on faults that have been ways, as we see to have taken place in the production of faults. get distortion in the mapped in the state are based on the recency of the last recog- Here we direction of the move- nized movement. ment, and waves are produced by the elastic force of the rock, it to its The following section briefly discusses when faulting was causing spring back from distorted form (Milne, recognized as the principal cause of earthquakes and how faults 1886, p. 47). were considered on early California geologic maps. The evolu- Though faults had long been noted in older rocks, as in the tion of fault maps of the state is then presented before going into a detailed discussion of the present Fault Map of California. case of displaced beds, early geologic maps mostly ignored fault Regional fault patterns are discussed, and the writer then pre- features or only noted an occasional fault. Individual U.S. Geo- sents his concept of structural provinces of California based on logical Survey folios for California (from 1894 to 1914) show no faults, or at two or three folio 1909. the predominant fault directions recognizable in the state. The most on a map before Fairbank's San Luis Folio shows several faults on cross relationship of faults to patterns of seismicity is discussed. Last- (1904) a section, but the faults are not his ly, other features depicted on the fault map, such as volcanoes shown on geologic map. and thermal springs and wells, are described and related to faults However, it appears to have been early U.S. Geological Survey where appropriate. policy not to show faults on the folio maps even if the geologists had mapped them as Fairbanks had done (Olaf P. Jenkins, personal communication, 1957). In 1909, the Santa Cruz foho

by Branner, Newsom, and Arnold was published, and it dis-

RECOGNITION OF FAULTING AS played many faults. Perhaps the Geological Survey changed its CAUSE OF EARTHQUAKES policy for this folio because the area it maps blankets a segment of the San Andreas fault zone, the importance of which had been dramatically demonstrated by the 1906 California earthquake. The understanding of earthquakes has come a long way since The San Francisco foho by A.C. Lawson, published in 1914, also Josiah Whitney, early State Geologist of California, considered portrayed many faults on the maps and on the cross sections. that ground fractures associated with the great 1872 Owens However, no faults are shown on Lawson's map of the San Valley earthquake were of small importance. The prevailing Francisco Peninsula, published in the 15th Annual Report of the thought at that time was that ground fractures were the result, U.S. Geological Survey (1893-94), although in the text the San not the cause, of earthquakes. Andreas and other faults are discussed at considerable length. As a matter of historical interest, it was not until 1819, in A perusal of other early geologic maps of areas in California connection with the Cutch, India earthquake of that year, that also reveals few mapped faults. The earliest volumes of the Uni- surface faulting itself was first recognized and well documented versity of California Publications in Geology show but few as accompanying an earthquake. In California, the first descrip- faults, albeit more than on the early U.S. Geological Survey tions of ground displacements associated with major earth- folios. Apparently, in early geologic mapping more attention was quakes were in 1836 on the Hayward fault and in 1838 and 1857 given to plotting the rock distribution than in trying to resolve on the San Andreas fault. However, descriptions of ground dis- geologic structure. placements during these earthquake-events were in newspaper accounts and were not made by trained observers. In fact, it was not until many years later that the connections between these earthquakes and these specific faults were recognized (Lawson, EVOLUTION OF FAULT MAPS 1908; Louderback. 1947).

In California it probably was LeConte who first proposed the OF CALIFORNIA idea of faulting as a cause of earthquakes. In his article "On the Structure and Origin of Mountains," LeConte (1878, p. 101) considered readjustment along the fault at the eastern base of the First Fault Map of the State— 1908 Sierra Nevada as the cause of the Owens Valley earthquake. Later, LeConte (1886, p. 179) stated that "With every readjust- The atlas of the State Earthquake Investigation Commission ment and increase of fault [movement] there is probably an report (Lawson and others, 1908) contains a map of California earthquake." Worldwide, according to Davison (1927), the first and the adjacent states, showing the more important known person to attribute an earthquake to the movement along a fault faults. This report and atlas were the result of the monumental probably was Rev. Fisher (1856) in his description of the Visp, investigation of the 1906 California earthquake which did such Switzerland earthquake. heavy damage in north coastal California. The fault map in the

What we now take for granted, that movement along faults is atlas is the first attempt to depict faults in California statewide the cause of most earthquakes, did not become generally accept- (Lawson and others, 1908, p. 346). The scale of the map is ed until after the 1906 California earthquake and H.F. Reid's approximately 1 inch equal to 30 miles, and the title is: "Geo- (1910) precise theoretical formulation of the elastic rebound morphic Map of California and Nevada with portions of Oregon theory. However, the English engineer Milne, anticipated Reid's and Idaho showing the diastrophic character of the relief, the DIVISION OF MINES AND GEOLOGY BULL. 201

is not well steep descent from the sub-continental shelf to the floor of the northward to about Cloverdale. The Calaveras fault Concord and Green Valley faults are Pacific, and the more important faults" —a cumbersome but located, but the shorter area are accurate description of the map. Plate lA (pocket, herein) is a recognized. Other faults correctly mapf)ed in the Bay fault. strange fault reduced version of this map identifying the faults described in the San Gregorio fault and the San Bruno A Pajaro the Lawson report. is shown directly cross-cutting the San Andreas at Gap is Lawson 19) as: (1) lying approximately Lawson's map is very interesting, for some of the faults shown and described by (p. on the axis of the geosyncline of Monterey Bay, (2) transverse on it were subsequently, and mistakenly, ignored on later maps. intersectng it, and near the place On Platel A, the San Andreas fault is shown extending about as to the San Andreas and (3) ceased. far south as San Gregorio Pass. The prominent portion of the where the 1906 surface mpture White Mountains fault San Andreas fault in the Mecca Hills, on the east side of Coa- In the east central part of the state, the chella Valley and on the east side of Salton Sea, had not been is recognized and extended as far south as the Coso Mountains. discovered. To the north, however, the Shelter Cove fault rup- In northem Califomia, the Mother Lode faults are totally ab- of their great antiquity and ture of 1906 is joined to the San Andreas where it leaves the sent, but probably this was because also not recog- mainland at Point Arena. This speculative connection, concealed complexity. The Mother Lode fault system was by the waters of the ocean and requiring a broad curve in the nized on several subsequent geologic maps of the state, including otherwise long straight stretch of the fault, was later thought to the 1938 Geologic Map of Califomia. be unreasonable, and the segments were not joined together on The fault along the Chico monocline is correctly depicted most subsequent maps. This lack of connection persisted until from its southem extent near Paradise, but it is drawn too far 1967 when sonic profiling at sea showed that the San Andreas north. By the time the second fault map of Califomia was pub- fault does indeed swing back to shore at Shelter Cove (Curray lished (Willis, 1922), only a small segment of this fault (east of and Nason, 1967). Red BlufO was shown (as a probable fault) . When the next map in this area. The Sierra Nevada fault is shown on Lawson's map as being (Jenkins, 1938) was published, no faults were shown rediscovered cut off at its southern end by the San Andreas fault at Gorman. Mapping for the Chico Sheet of the Geologic Atlas faults only show Actually the Garlock fault, as we know it today, intersects the these faults (Burnett, 1963). Admittedly, the the San Andreas fault at Gorman and also intersects the Sierra small displacements, but their continuity and abundance on Nevada fault northeast of the town of Mojave. The Garlock fault crest of the monocline are very striking on aenal photos and are also extends far eastward into the southern Death Valley area. also very interesting in that they are aligned with the active southeast. The Mojave Desert on Lawson's map is, as we might expect, Foothills fault system to the Sur- shown as being devoid of faults, for little of the desert land had Lawson correctly shows the Honey Lake fault and the been explored or even mapped topographically by 1908. The prise Valley fault in northeastem Califomia. He also noted northern extent of the Sierra Nevada fault is shown as an almost other important faults in this part of the state, but owing to lack continuous trace following the eastern side of the Sierra Nevada of adequate maps and only crude reconnaissance studies, mis- crest past Lake Tahoe and into Plumas County. Modem detailed connections were made. The same is true of the northwestern at its mapping shows that this continuity is a gross oversimplification. part of the state. The Orleans fault was recognized Lawson described (p. 19) a "San Gabriel branch of the San northemmost extent (where it crosses into Oregon), but unhke Andreas fault" in southern California heading westward to the the simple curving line depicted, the Orleans fault to the south ocean at Carpinteria. This fault line quite accurately connects is now known to take a much more circuitous route, befitting a what are now known as the Cucamonga, Sierra Madre, Santa low-angle thrust fault, before continuing for many miles to the this fault, Susana, and Oakridge faults. What is mapped as the San Gabriel southeast. Actually the southem two-thirds of about is correctly fault today lies farther north, within the San Gabriel Range, and 145 km (90miles), in extremely rugged terrain, quite then heads northwestward, joining the San Andreas near Gor- located on Lawson's map. Just west of this fault, is O.H. Her- man. shey's "Redwood Mountain" fault (Lawson and others, 1908, p. The San Jacinto and Elsinore faults are crudely depicted on 17). This corresponds to the South Fork Mountain fault of the Lawson's map, but the Whittier and Malibu-Santa Monica faults Geologic Atlas. are quite accurately drawn. It is interesting to note that faults were not depicted on any The Kern Canyon fault is quite accurately located, and Law- of the state geologic maps preceding Lawson's 1908 fault map son's map, unlike several succeeding maps, shows its full north- (see Section II, herein), nor were they shown on the 1916 geo- em and southem limits. A prominently depicted fault west of the logic map of Califomia. G.A. Waring (1915), in describing the to Kem Canyon fault is not recognized on later geologic maps. springs of Califomia, tried to show the relationship of springs Some other important faults in the southem part of the state faults in the state, but a note on his map indicates that the faults that were mapf>ed at that time (at least in part) include the San were taken from the atlas accompanying the 1908 State Earth- Clemente Island, Santa Ynez, and Nacimiento faults. quake Investigation Commission report.

In central Califomia, Lawson (1908, p. 19) described a "Santa In 1916, Harry O. Wood, in a study of faults in Califomia as Lucia fault" as "one of the dominant structural lines of the Coast generators of earthquakes, published a modified version of Law- Ranges at the base of the Santa Lucia Range on the border of son's 1908 fault map (Wood, 1916). This map, (Plate IB, here- Salinas Valley." Today wc know the northern part of this struc- in), confined itself to Califomia, but omitted a number of valid tural line as the King City fault. Lawson shows this fault con- faults shown on Lawson's map. Wood added five faults or tinuing southeastward to San Miguel. This part is incorrect "lines" which he considered "generatrices of earthquakes." Per- according to modem maps, which show the King City fault as haps the most interesting (and prophetic) was his so-called "Eu- a possible continuation of the Rinconada fault somewhat farther reka-Ukiah-San Pablo line." This appears as a northwestward to the west. continuation of the "Haywards" fault along the Rodgers Creek,

In the San Francisco Bay area, the Hayward fault is correctly Healdsburg, and Maacama faults, extending all the way to Eu-

depicted, but its north-bay counterpart, the Rodgers Creek- reka as similarly proposed by Herd ( 1979) and Jennings (here-

Healdsburg fault, is missing. However, in the text, Lawson in). Two other lines, lying offshore, Wcxxi referred to as the

(1908, p. 17-18) discusses the prolongation of the "Haywards" Monterey and San Pedro submarine fault zones, but they do not fault on the cast side of the Santa Rosa and Russian River Valley correspond to any of the offshore faults recognized in recent — —

1985 TEXT TO ACCOMPANY THE FAULT AND GEOLOGIC MAPS OF CALIFORNIA

years by acoustical profiling. Wood's "Mare Island-Nevada-Car- compiled by Wood. In the central Coast Ranges, for example, son line" was delineated on the basis of rather inaccurate loca- more than half of the faults are shown in the "active" fault tion of earthquakes, but this northeasterly trend does not category. The legend for the southeast sheet specifies that the correspond to any faults known in the surface or subsurface "active faults" have "earthquakes recorded on lines so marked." today. It is, however, parallel in part to the subsurface Stockton Such faults indicated include the Owens Valley, San Andreas, fault across the Great Valley. The fifth feature or "line" added Newport-Inglewood, San Jacinto, and parts of the Elsinore and by Wood is the "Great Valley axis" lying on the east side of the Chino faults. The "dead faults" are designated as "not known to Valley and approximately bounding the Sierra Nevada block. have been active during historic time." "This line," Wood (1916, p. 79) states, "is not considered to Plate IC is a greatly reduced and somewhat generalized version delineate, even crudely, any fault zone or chain of faults, of the Willis and Wood map, but it accurately represents most simply to bring to notice the tendency for certain meizoseismal of the faults shown on the 1922 map. In many ways the detail areas to cluster in line along the Valley." An inspection of recent- of the Willis and Wood map goes far beyond Lawson's 1908 ly published earthquake epicenter maps, however, does not seem map, not only by virtue of the much larger scale, but more to bear out Wood's statement. importantly because, during the 14 years following the Lawson map, faults and the problem of locating and understanding them received much more attention than Second Fault Map of California— 1922 before, not only from seis- mologists, but also from geologists searching for petroleum and other mineral resources and from geology professors and their Bailey Willis, Professor of Geology at Stanford University, students in the two leading academic institutions then in the and H.O. Wood, Research Associate in Seismology of the Carne- state, the University of California and Stanford University. Un- gie Institution of Washington, prepared a new fault map of fortunately, the map is totally blank in the northernmost part of California that was published by the Seismological Society of the state where the earlier map by Lawson showed a surprising America in 1922 as a separate publication. The map was com- amount of information on faults that has, in most instances, piled at 1:506,880 scale (1 inch equals 8 miles). A reduced withstood the test of time. Willis (1923, p. 6) justifies the ab- version of this map is portrayed in Plate IC (in pocket). The sence of fault delineation north of the latitude of Santa Rosa by Willis-Wood map is evidence of the growing concern about explaining that topographic maps showing sufficient detail and earthquakes in California; Willis (1923a) reports that the busi- accuracy of the landscape did not exist and that, therefore, it was nessmen of San Francisco subscribed $1,600 for the pubhcation impossible to follow and plot the faults except by an expenditure of the map. The publication of the map was followed by a text of time and money beyond the project's means. Willis intention- (Willis, 1923b) which attempts to explain the rationale in com- ally disregarded Lawson's map. (Perhaps his professional feud piling the faults and includes a brief discussion of earthquakes with Lawson influenced his decision—this is suggested by his and their relationship to faults. (Wilhs' strong feeling on the reference to the map in Lawson's Earthquake Commission re- importance of this relationship is evident in the opening sentence port of the 1906 earthquake as "a map of the principal earth- of his text, which reads: "Another title, and perhaps a more quake faults of California but on a small scale and not complete obvious one, would be 'Earthquake Map of California.' ") A enough to be of practical use.") large part of the report is also given to description of various The Willis and Wood fault classification was highly interpre- fault features, which includes a particularly long treatment of the tive and commonly went beyond the data at hand. The attempt physiography observed along the San Andreas rift. was certainly too ambitious; even today, distinguishing between Willis was responsible for compiling the northern part of the "active" faults and "probably active" or "dead" faults may still state, that is, the part north of San Luis Obispo, while Wood be beyond our means. Nevertheless, as a map showing the loca- prepared the southern part (Willis, 1923, p. 4). An attempt was tion of faults known in the state at that time, the 1922 map made to identify "active faults," "probably active faults," and contains a wealth of information, some of which even goes "dead faults." However, Willis' criteria for classifying faults beyond maps published later. were not the same as Wood's criteria. Willis considered any lault The remarkable advancement in fault mapping represented by related to "a growing mountain" as a reasonable subject for an Willis and Wood's 1922 fault map (Plate IC) becomes readily active fault. The method, as he explains, was based on observa- apparent when it is compared to Lawson's 1908 map (Plate lA). tion of "mountain forms" and the interpreted age of topographic In the Coast Ranges province, for example, the 1922 map shows surfaces and old landscapes. In this way, he classified numerous numerous faults—including the Rodgers Creek-Healdsburg, the mountains as being bounded by active faults. Wood, on the other Tolay, the Burdell Mountain, the Pilarcitos, the Butano, the Ben hand, considered active faults as those that are known to have Lomond, the Tesla, the Ortigalita, the Sur, the Tularcitos, the had some movement during historic time or those for which Rinconada, the Ozena, the Little Pine, and the Pleito faults there is evidence of recent surface dislocation. The map has two which are not shown on the earlier map. Also, in this province, different legends for the three sectional sheets of the state to such unnamed faults as those at Dunnigan Hills and in Capay clarify this difference in interpretation of "active faults." The Valley are correctly shown on the 1922 map but not on the northwest sheet (which was entirely the work of Willis) and the earlier one. southwest sheet (a joint effort) contain the following note in the Wilhs and Wood's map remains an informative source even legend: today. The map shows, for example, an "active fault, uncertainly located," lying west of and parallel to the San Andreas fault and North of San Luis Obispo faults are shown as active if coincident with the straight coastline from Bodega to Point there has been an earthquake during historic time and also Arena. Today the existence of this fault is a likely possibility, wherever they define valleys, ridges, or ranges which are although confirmation of it is still lacking. Another interesting now growing, even though there is no record of an earth- feature shown, in a critical area, is the Dry Creek fault at the quake on that particular fault during historic time. Warm Springs dam site. According to Willis and Wood, this is an "active, well located" fault which connects (to the north as Consequently, that part of the map compiled by Willis shows well as to the south) with "probable faults, character and loca- many more "active" and "probably active" faults than the area tion uncertain." Today part of this fault is recognized and ap- 10 DIVISION OF MINES AND GEOLOGY BULL. 201

pears on recent U.S. Geological Survey maps (Blake and others, of the area is still largely unmapped on the 1922 map, as it was 1974), although the connection between the Dry Creek fault and in Lawson's time. the active Rodgers Creek fault, which is shown on the 1922 map, North of the Garlock fault, in the southern Sierra Nevada, the has not been verified. To the north, faults arc shown in Anderson Sierra Nevada-Owens Valley faults are quite accurately located; Valley and along the Navarro River—areas which since 1922 the Kern Canyon fault, however, is incorrectly shown as being have not been cntically evaluated for active faults. To the south, shorter than depicted by Lawson; and the White Wolf fault, the Quaternary faults now recognized at San Simeon are shown which ruptured during the 1952 Arvin-Tehachapi earthquake, is as "active." Interestingly, an "active fault, well located" is shown, although only as a "dead, well-located fault." liast of the shown in the San Luis Range, at Diablo Canyon; however, recent Sierra, only a part of the Death Valley, Panamint, and Furnace investigations in this area have not confirmed it. The Hayward, Creek faults are recognized. Several other probable faults are Calaveras, and parts of the Nacimiento fault zones are shown shown bounding valleys and steep mountain fronts, but few of much as they have been mapped since then. The major Quater- these have been confirmed by later mapping. nary faults in the central and southern Coast Ranges as we now Like Lawson's map, Willis and Wood's map shows no faults know them were all recognized by Willis and Wood, perhaps in the Mother Lode of the northern and central Sierra Nevada. with the exceptions of the San Juan fault and the full extent of This is interesting because a close examination of the text of the Rinconada fault zone. Of course, they had no idea of the some of the U.S. Geological Survey Mother Lode District folios offshore continuations of the Seal Cove-San Gregorio-Palo Colo- —for example, Ransome (1900) —reveals that early geologists rado faults or the Hosgri fault zone lying offshore of San Luis were aware of abundant faults in the area and that, furthermore,

Obisf>o County. Also, they did not always recognize certain some believed that such faults were possibly still active. For Coast Range faults as being young faults, for some are shown as example, Ransome (1900, pp. 7-8) writes: "dead" faults.

Of all the areas shown on the 1922 map, the Transverse It appears highly probable that much of the movement Ranges and the Los Angeles basin are depicted in greatest detail. which has affected the Sierra Nevada since the close of Therefore, the 1922 map shows numerous faults in these areas Jurassic time.. .has resulted in the linear fissure system of not recognized on Lawson's map, including the northern part of the Mother Lode. the San Gabriel, the San Francisquito (site of the St. Francis Dam failure), the Arroyo Parida, the Red Mountain, the Simi, The dislocations by which the fissures were originally the Newport-Inglewood, the Palos Verdes, the Cucamonga, and opened, were of the kind known as thrust faults.* The the Sierra Madre faults. On Willis and Wood's map the Pacifico present structure of the veins shows that the original dis- and Santa Ynez faults are shown more accurately than on Law- placement was followed at intervals by further movement son's map (although still somewhat crudely). The Liebre and of the same kind. There has very probably been subordi- Clearwater faults are recognized but incorrectly joined together. nate displacement of reverse character, i.e., downward Willis and Wood classify the faults shown in the Transverse movement of the hanging wall relative to the foot wall, Ranges as "dead" with the exception of the San Andreas fault producing local crushing of earlier-formed veins, and re- (which transects the Transverse Ranges) and a concealed fault sultmg m more bodies of irregular and brecciated charac- in the Alamo area along San Antonio Creek in the Santa Maria ter. There is evidence that this latter movement is still in basin. This latter fault, shown as an "active fault, uncertainly progress, producing the gouges and slickensided surfaces located," is not recognized by later mapping in the area (for which accompany most of the veins. example, Woodring and Bramlelte, 1950) and therefore, is not shown on the 1975 Fault Map of California. The fault was The fissures which the veins fill were formed after the apparently based on a doubtful fault hypothesized by Arnold post-Jurassic folding in of the bed-rock complex and after and Anderson (1907) and was probably viewed by Willis and the granitic and dioritic intrusions. They have probably Wood as the cause of the rather severe 1902 and 1915 "Alamo" continued to be a zone of movement and readjustment ever earthquakes. Willis and Wood likewise classify as "dead" all the since their first dislocation, and such movements are still faults in the Los Angeles basin, with the exception of the New- in progress. port-Inglewood and Chino faults. the faults and "fissures" were not plotted On close inspection, one can make out the San Fernando fault, Why Mother Lode on which the disastrous earthquake of 1971 occurred. However, on the folio maps— whether because of L'.S. Geological Survey policy or of difficulties in the structural com- Wood has identified this fault as a "probable fault, character and because mapping location uncertain." Nevertheless, other available geologic maps plexities— is not known. In any event, no attempt was made to show this important and extensive fault system, even in a most of the San Fernando area prior to the 1 97 1 earthquake show little until very later (see indication of a San Fernando fault. general way, on any regional map much p. 11). In the Peninsular Ranges a large number of faults are shown. Among these, the San Jacinto, Elsinore, and Whittier faults are better defined than on the 1908 fault map. The Chino fault is Faults Shown on Geologic Map depicted as a "probable active fault," presumably on the basis of of California— 1938 earthquake epicenters. A probable fault is correctly shown in the upper part of the San Diego River, but many other "probable A far more accurate depiction of faults in California appears faults" m the southern California batholith are today considered on the 1938 Geologic Map of California, compiled by Olaf P. to be joints in granitic rtKksand not faults (on the basis of a close Jenkins at a scale of 1:500,000. This outstanding map of its time, examination showing that they have no displacements). The however, followed conventional compilation practice, whereby Crislianilos fault and a fault m Palm Canyon by Palm Springs all faults arc treated alike and historic or recently active faults arc mapped more or less as they would be today. are not distinguished from any other faults shown on the map. The Mojave Desert is shown largely devoid of faults. The

northern boundary, the Garlock fault, is recognized, but the rest *Wc would refer lo ihese Taults today a& high-angle reverse faults. 1985 TEXT TO ACCOMPANY THE FAULT AND GEOLOGIC MAPS OF CALIFORNIA 11

Plate ID is a reduced version of the 1938 geologic map showing gists as Knopf (1929) and Ferguson and Gannett (1932) had just the faults. not only recognized the abundant fault fissures in which the Jenkins did not refer to either the Lawson fault map or the gold-quartz veins were emplaced, but also had talked about the Willis and Wood map, because he had much more recent data existence of a major through-going reverse fault bordering the to choose from for most parts of the state. In some ca.ses he could Mother Lode region on the east. These faults are not shown on

have profited by selective use of certain faults from these earlier any of their regional maps but the segments which lie in the areas fault maps, but he may have chosen not to do so because of that they mapped in detail are shown. Then, in 1944, King and possible problems with harmonizing the earlier mapped faults others defined a highly generalized fault trace identified as the with the geologic contacts he was depicting. Jenkins rightly "Mother Lode mineralized fault" on the Tectonic Map of the could not mix faults and geologic contacts without additional United States. Sixteen years later, Lorin Clark, taking the find- field evaluation, for which he had neither the time nor the funds. ings of the early gold-belt workers and adding his detailed obser- In addition, the small scale of the Lawson map and its crude vations, prepared a regional map defining the Foothills fault shaded-relief base, would have posed serious problems in some system (Clark, 1960). His map shows the Foothills fault system places in locating features on the larger and much more accurate bounded on the east and west by what he named the Melones 1938 base map. fault zone and the Bear Mountains fault zone, respectively. Sev- A comparison of the 1938 map with the 1922 map shows that eral years later Lorin Clark's fault system appeared on the Base- in the Coast Ranges, a few faults that were not shown on the ment Rock Map of the United States, compiled by the U.S. 1922 map were added, but others were omitted. The major Geological Survey and the University of Texas (Bayley and Rodgers Creek-Healdsburg fault is missing, but the less pro- Muehlberger, 1968) —although mislabeled as the "Mother Love nounced Tolay fault is shown. The Hayward fault falls short of Belt"! The recency of fault activity on faults within the Melones San Pablo Bay at its north end. The Concord fault is shown as fault zone, was recognized on the detailed maps by Eric and

before, but its counterpart north of Suisun Bay, the Green Valley others, (1955, Plate I and p. 27). They note that movement took fault, is missing. The Palo Colorado and Sur faults were added, place following the formation of the Table Mountain Latite, and the controversial King City fault was omitted. suggesting late Pliocene or even Pleistocene activity. Much more Some of the more important faults in the northern part of the recent investigations involving trenching (Alt and others, 1977) state that the 1938 map shows, but that the 1922 map does not, have shown that Holocene activity, including fault-displacement include the Surprise Valley and Honey Lake faults and the faults of soils has taken place. Thus, Ransome's intuitive observations of the Lake Tahoe graben. Absent from the 1938 map are the 77 years ago concerning the recency of fault movement men- series of faults now known to be associated with the Chico tioned earlier, have proved to be correct. monocline, which are indicated on the 1922 and 1908 maps.

In the Transverse Ranges, the Santa Ynez fault is better de-

fined, as is the Clearwater, but the Big Pine fault still had not

been discovered. The San Gabriel fault is correctly shown at its Combined Wood and Jenkins north end, disappearing under the Frazier Mountain thrust fault, and the south end is correctly shown terminating at Mt. Baldy. Fault Map of The The Malibu-Santa Monica fault (shown on the 1922 map) is left Southern Half of the State— 1947 off, but the Raymond Hill fault is correctly shown, as well as the Sierra Madre-Cucamonga faults. A vast improvement is shown where the San Andreas splits into two branches and becomes In 1947, Harry Wood published in the Bulletin of the Seismo- entwined with the Banning fault. Also, the Pinto Mountain fault logical Society of America a paper entitled "Earthquakes in

was recognized for the first time, and the Santa Rosa Island and Southern California with Geologic Relations." In it he tried to Santa Cruz Island faults were added. correlate earthquake origins in California with geologic faults. On the 1938 map the myriad ofjoints shown in the Peninsular To illustrate his ideas, he took the faults shown on the southern Ranges on the 1922 map have been omitted although the Temes- half of the 1938 Geologic Map of California and supplemented

cal fault has been preserved. It is difficult to see the Newport- it with faults he had shown in the same area on the 1922 Fault Inglewood and the Palos Verdes faults, which are there, at least Map of California. Wood also added certain faults not known by in part. The submarine San Clemente Island fault, although him before and also not shown on Jenkins' 1938 map. Wood, known at the time, is not shown, probably because no faults were being primarily a seismologist, had J. P. Buwalda, Professor of shown off the coast on the 1938 map except where they happened Geology at the California Institute of Technology (with which to intersect islands. A more correct orientation of the Rose Wood was then associated), critically examine the resulting fault Canyon fault near San Diego is shown. map. The published map, from which Plate IE is patterned, was Some faults are shown in the Mojave Desert, signaling the then used to plot epicenter locations, their relation to the faults beginning of recognition of a strong northwest structural grain, serving as the basis for the paper. Choosing an approach to fault but the area at this time was still largely unmapped. classification more cautious than the one used by Willis and Very little of the configuration of the Sierra Nevada fault Wood on the 1922 map, with its "active," "probably active," and shown on the 1922 map is shown on the 1938 map, and definition "dead" designations. Wood designates the faults on his map as of this fault's southern end is almost nonexistent. The faults in "major faults" and "other faults," and classifies each fault as Owens Valley (except for the 1872 break at Lone Pine) are not "well located," "approximately located," or "uncertain." as completely defined as on the 1922 map. The northern extent A comparison of Wood's 1947 map with both Jenkins' 1938 of the Kern Canyon fault, correct on Lawson's map, falls far map and Willis and Wood's 1922 map shows that Wood resur- short on the 1938 map. Not until new mapping by the Division rected possibly significant faults from the 1922 map which do of Mines and Geology for the Fresno Sheet of the Geologic Atlas not appear on the 1938 map and also that he added some faults was this fault depicted correctly again on any published map that do not appear on either the 1938 or the 1922 maps. (Matthews and Burnett, 1966). Among the features that Wood carried over from the 1922 As mentioned in a preceding section, faults in the Mother map but that do not appear on the 1938 map are the King City Lode still were not depicted. By this time, such prominent geolo- fault and faults in the vicinity of Diablo Canyon and Los 12 DIVISION OF MINES AND GEOLOGY BULL. 201

Alamos.' The joints in the southern California balholith east with thin blue lines, does not distinguish among the faults as far and northeast of San Diego arc retained as probable faults, but as recency of movement is concerned. It is a product of the later invesligaton; have found no evidence for displacement on Division's Earthquake Catalog Program. A short text is included most of these features and have concluded they are not faults. on the face of the map. The fault in Palm Canyon, by Palm Springs, which the 1*538 map docs not show, is correctly retained from the l')22 map. Small-Scale Fault Maps of California Among the significant omissions on the 1947 map are the Big Pine fault and the San Juan fault —both known today as major Several page-size and smaller outline maps specifically show- Quaternary faults. The configuration of the Banning and Mis- ing the major and/or active faults of the state have been pub- sion Creek faults is much improved in the manner of the Jenkins' lished over the years. Some of the more noteworthy ones are compilation, but a significant departure exists with the projected listed below: location of the San Andreas fault in the Salton Sea area (which still is largely a matter of conjecture). The Inglewood fault is • Richter, C.F., 1958, Elementary seismology, W.H. Free- more continuous on the 1947 map, and the Palos Verdes fault man and Co., and Francisco, p. 441 (Figure 27-3). is shown as a splinter off the Inglewood fault. The Imperial fault, • Dickinson, W.R., and Grantz, A., 1968, Historically and with offset along some 64 km (40 miles) of the fault trace during recently active faults of the California region, /n Proceedings the May 1940 earthquake, is added. Many other differences in of conference on geologic problems of San Andreas fault detail occur between this map and the earlier ones, and the 1947 system: Stanford University Publications in the Geological map is without doubt the best fault map of the southern part of Sciences, v. XI, (map and list following p. 374). the state published up to that time. • U.S. Geological Survey, 1970, Active faults of California, (map and text, p. 15), information pamphlet (revised and Earthquake Epicenter and Fault Map updated periodically; latest revision, 1974). of California— 1964 The scale of these maps and the grossly simplified bases used, In 1964, the California Department of Water Resources com- however, make it almost impossible to locate the faults except in piled a fault map of California using mainly the published and the most general way. unpublished 1:250,000 scale geologic atlas sheets of the Califor- In addition to the small-scale maps discussed above (faults of nia Division of Mines and Geology (Hill and others, 1964). which are almost all well documented), an interesting fault map Although this map depicts faults, its primary purpose was to of the state, particularly of the Coast Ranges, was published by show epicenters, and the bulk of the report accompanying the Bruce Clark in the Bulletin of the Geological Society of America map consists of a catalog of epicenters (magnitude 4 and greater, (1930). Clark, a Professor of Paleontology at the University of from 1934 to 1961 ). The faults shown were divided crudely into California, Berkeley, was intrigued with the tectonics of the "active faults" (after C.F. Richter's textbook "Elementary Seis- Coast Ranges, which he interpreted as a complex series of fault- mology," 1958), and "other faults, activity not ascertained." ed blocks. To illustrate his ideas he prepared a map of what he The criteria used to distinguish between these two classes are not considered to be the "pnncipai known primary faults" in the indicated on the map, nor are they explained in the text. All the Coast Ranges (Figure 3). faults on this map are shown in red and, according to the legend, As was common in those days, Clark mterpreted the faults in the two classes of faults are represented by two different line- the Coast Ranges, not as large-scale strike-slip faults, as we do widths; unfortunately, the map shows a range of line-widths, today, but as bounding a series of raised and depressed blocks. making it difficult to determine in some cases whether the fault Clark indicates in his text that the data for his map came from was meant to be designated as active or not. various published and unpublished maps and that a large num- The map was published on three sheets at 1 :5(X),(X)0 scale and ber of the fault lines were studied in the field by either himself is included in the pocket of the California Department of Water or his assistant James Fox. Clark states (p. 70) that "only faults Resources Bulletin 1 16-2. The map and report were prepared as which we considered definitely proven, by either direct or in- part of a "crustal strain and fault movement investigation," for direct methods, have been included." Of course, "indirect meth- use in planning studies and tinal design stages of water resources ods" leaves much room for interpretations that may not always development in the state. The report recognized the usefulness be accepted by other geologists. A close look at the map shows, of such data in preparing estimates on the probability of earth- however, that solid lines represent "accurate" faults and that quake occurrence and the magnitude of the damaging earth- these comprise less than half of the faults shown on the map. quake forces that should be anticipated at sites proposed for Dashed and dotted lines indicate "approximate" and "buried" construction of authorized State water facilities. faults, respectively, and most of these must have been deter- mined by Clark's "indirect" methods. Many of them, in light of Earthquake Epicenter Map later detailed field mapping, have been modified or discredited, but some have proved to be correct or are still considered possi- of California — 1978 ble. For example, his interpretation of a Salinas Valley (his no.

10) and King City (no. 1 1) faults as branches of the San An- fault The California Division of Mines and Geology published an dreas ( 1 ) has not held up. But his extension of the unnamed earthquake epicenter map of California, known as Map Sheet known today as the White Wolf fault across the southern San 39 (Real and others, 1978). This 1:1,000,000 scale map shows Joaquin Valley to the San Emigdio fault (23) was substantiated all epicenters of magnitude 4 or greater from 1900 through 1974. in a dramatic way by the occasion of the Arvin-Tehachapi earth- Faults shown on the map arc reduced from the Division's 1975 quake of 1952 and the a.ssociated ground rupture. In like man- Fault Map of California The map, which represents all faults ner, Clark's northward extraptilation of the Hayward fault (3)

state •The |j»i AUntcM fault u alio najnrd on ui MxompjinyinK map by Wood (his map No. 4> . here, although shown concealed, it is identified as one of the major faults of the Perhaps thu tuipectr

Figure 3 Bruce Clork's 1930 mop of Colifornio showing "principol known primary foults". [From Geological Society America Bulletin, V. 41, pi. 161. 14 DIVISION OF MINES AND GEOLOGY BULL. 201

into Marin and Sonoma counties is recognized today, although In 1971, a preliminary version of the geologic map including his northernmost arcuate extension into Mendocino County may classified faults was completed. It appeared as two sheets in the

not exist, or if it does, at least not as part of the same Hayward- pocket of a limited edition of a report financed by the U.S. Rodgers Creek-Healdsburg-Maacama fault trend we know to- Department of Housing and Urban Development entitled "Ur- day. ban Geology Master Plan for California" (Bruer, 197f).* This As an interesting sidelight we might point out that what is now highly preliminary map was then revised, and review copies were known as the South Branch Garlock fault was earlier known as prepared in 1972. After the reviewing process was completed and the Antelope fault (57). Note also that Clark's Sisquoc fault changes and additions were made to the compilation, a prelimi- (34) extrapolation to the San Luis Hills area across the Santa nary version of the map was prepared and published rapidly in Maria Valley resembles Clarence Hall's east-side bounding fault order to satisfy the growing demands for fault information by the of his proposed Lompoc-Santa Maria pull-apart basin (Hall, cities and counties that were faced with the preparation of a new 1978). The reader can make other interesting compansons with seismic safety element for their General Plans, as required by the earlier and later fault maps illustrated in this bulletin. State. As a result, Preliminary Report 13, "Preliminary Fault and Geologic Map of the State of California" was published in Preliminary Fault and Geologic Map 1973. The map was printed on two sheets at 1 :750,000 scale ( 1 inch of California— 1973 = 12 miles). The map showed faults offshore as well as on land. Special symbols and notations on the map indicated: (1) seg- As an integral part of the new 1:750,000 scale Geologic Map ments of faults with observed historic surface displacement, (2) of California, which was planned in 1965, the writer proposed points of fault creep slippage, (3) direction of fault dip, (4) that faults be emphasized and that relatively recent faults (those direction of relative lateral movement along faults, and (5) rela- with known historical movement or with known offset of Qua- tive up or down movement of individual faults. The map proved ternary beds) be appropriately indicated. This innovation in to be useful not only to planners but also to geologists and depicting faults was designed to help satisfy the numerous re- seismologists, engineers, and others involved in assessing the quests the Division was receiving for a map showing the "earth- possibility of future fault activity and ground rupture in various quake faults in the state." Thus a three-fold fault classification parts of the state. system, based on recency of movement, was devised and utilized. In an attempt to be as specific as possible and to avoid the problems arising from various definitions and understandings of FAULT MAP OF CALIFORNIA the term "active fault," faults were subdivided into three catego- ries, based on the time-scale universally used by geologists and — 1975 EDITION seismologists. It was felt that this system was commensurate with the scale of the map used and was also realistic within the The Preliminary Fault and Geologic Map of California, 1973, time-frame considered for preparing a statewide compilation. proved to be in such great demand that the printed supply was The three categories of faults chosen for the statewide compila- soon exhausted. In the meantime, the fault information on the

tion were: ( 1 ) faults along which historic displacement has oc- preliminary map was further edited for a new edition, and new curred (red color), (2) faults having Quaternary displacement, data were added in several areas, especially offshore. Then the but without an historic record of movement (orange color), and locations of some 584 thermal springs and wells were added. The (3) faults that are pre-Quatemary in age or for which no Quater- resulting new edition measured about 1.4 by 1.5 meters (4.5 by nary movement has been recognized (black). This fault classifi- 5 feet) and was printed in six colors. Each historic fault, shown cation system made this the first statewide map to depict faults as a red line on the map, was emphasized with a narrow pink by recognized recency of movement. band. Among the Quaternary faults, shown as orange lines, pale

* this In lame report, a page-size provisioiial fault map of the state was included as Figure A-6 (original compilation scale was 1:1,000,000) . This map. compiled by J.E. Kahle, attempted to document the type and kind of stirface faiJting associated with historic ground breaks.

Tab/e 1. Summary of published fault maps of California.

TITLE 1985 TEXT TO ACCOMPANY THE FAULT AND GEOLOGIC MAPS OF CALIFORNIA 15

orange bands were added to identify the major Quaternary Lastly, red dots on faults indicate where fault creep has been or faults. The map was published in 1975 in a new series. It was is being measured. All these special notations are described in designated as Geologic Data Map No. 1, and entitled "Fault more detail below. Map of California, with Locations of Volcanoes, Thermal Springs, and Thermal Wells." Fault Classification Depiction of Faults In 1965, when plans were being made for a 1;750,000 scale

Among the multitude of faults shown on the State Fault Map, geologic map, it was decided to show more than the usual infor- many have lengths of tens or hundreds of kilometers, and cumu- mation about faults on a state map by indicating some informa- lative displacements of kilometers or even scores of kilometers. tion about each fault's history. A way of doing this would be to

For example, there is considerable evidence to postulate hun- classify faults according to their recency of activity. At that time dreds of kilometers of right-lateral displacement on the San An- (as at present), there was little agreement as to what "active faults," "potentially active faults," and "inactive or dead faults" dreas fault since its inception, and 25 to 64 km ( 16 to 40 miles) of left-lateral displacement on the Garlock fault. Also, we know were, so these terms were deliberately avoided.* In their place, that the Sierra Nevada block was raised several thousand meters a fault classification system was developed that permitted the during the late Cenozoic era. In addition, it appears that, as a presentation of fault information that was as factual as the geo- result of subduction, rocks of the Franciscan Complex have been logic data would permit and that still included some indication dragged far below the rocks of the Great Valley Sequence along of the relative degree of fault activity. the Coast Range thrust. The three-fold fault classification scheme devised distin- On the other hand, many other well-known faults have rela- guishes faults entirely on the basis of recency of movement. The tively small displacements, even though the fault length is meas- first category includes those faults on which recorded displace- urable in tens or hundreds of kilometers. Furthermore, many of ment of the surface of the earth has taken place in historic time the faults shown on the Fault Map are comparatively minor. during earthquakes or by fault creep. In California, historic time Some geologists have questioned the advisability of showing mi- is about two hundred years, a very short interval indeed, in any nor fault features, contending that they contribute little informa- geologic sense. The historically active faults are shown in red tion and "clutter" the state fault map. These suggestions are with a pink border for emphasis. The second category includes valid for certain map uses, but they are not in keeping with the those faults that have displaced Quaternary deposits (the latest original map objective of recording all fault features in as much geologic epoch, which includes approximately the past two mil- detail as our data allowed and within the limits of legibility. In lion years), but that have no historic record of surface displace- this way the map would serve as a dependable source of back- ment. These Quaternary faults are shown in orange, with the ground fault data for the state as a whole, which could be eva- major faults and fault zones emphasized by a pale orange band. luated and interpreted in the future by more detailed studies. Faults in the third category, designated by heavy black lines on

Further, it was felt that by recording faithfully all mapped the map, are those without reccign/zec/ Quaternary displacement. faults, no matter how short or isolated they might appear, future Probably most of these are Pliocene or older; but many are of mapping might show possible fault extensions or reveal a fault unknown age, and some of these may have had unrecognized zone. The writer has been impressed ever since his student days Quaternary movement. that there are many faults that are plainly visible in underground The pink and orange bands on the historic and major Quater- mine workings that cannot be detected on the surface even after nary faults are for emphasis only. The width of the bands has no close scrutiny. Indeed, the discovery of many previously un- particular significance. They are not to be confused with the known faults during exploratory trenching shows that there are special studies zones of the Alquist-Priolo Special Studies Zones many more faults in California than heretofore expected. Act, which requires the State Geologist to delineate zones en- The prime users of such a statewide inventory of faults are compassing all potentially and recently active faults. (These engineering geologists and others who have responsibility for study zones maps are available separately from the California siting critical structures such as dams, nuclear power plants, and Division of Mines and Geology.) any other large, potentially hazardous engineering works. However, land-use planners and lay people concerned with ac- tive faults and earthquakes are also interested in such data. The Fault Definitions numerous calls and inquiries for additional information about the faults shown on the map are continual testimony to the Before proceeding further, it will be useful to discuss the correctness of our decision to show faults in such detail. definition of "fault" and such terms as "active," "potentially In addition to showing the location and extent of faults with active," and "capable," because these terms are often used with- lines color-coded to indicate recency of activity, the map indi- out a clear understanding of them. In recent years, especially cates the relative movement on faults (where this is known) with since the siting of nuclear power plants, consideration of poten- symbols. Arrows indicate the direction of relative lateral fault tially hazardous faults are of special concern (and the subject of slippage; the letters U and D indicate relative vertical (up and extensive investigations, reports, and hearings). A definition of down) fault slippage; and barbs on a fault indicate the upper terms, therefore, is essential to make common understanding plate of low-angle reverse or thrust fault. An arrow at right possible, not only among geologists, but also between geologist angles to the fault trace indicates the direction the fault surface and lawyer or geologist and lay people involved in planning dips. Dates placed alongside the historic faults indicate when decisions. Numerous reports contain fault definitions, and some earthquakes occurred that were accompanied by fault rupturing, of the most pertinent definitions recently have been summarized and symbols indicate the extent of the earthquake fault rupture. by Slemmons and McKinney (1977).

Miiny dcniiitions of thoM: lypt'5 uf faults have been published, some of which are widely andesen legally recognized. Howes er. in most of Ihese cases j purpose has to be slated first —for example, construction of a nuclear power plant, a large dam. or a hospital —Ix'fore a specific fault definition can be applied. This problem is discussed more fully in the following section. 16 DIVISION OF MINES AND GEOLOGY BULL. 201

In defining the term "fault," geologists have no significant ing Quaternary time (last two to three million years)" (Hart, disagreement; the various defmilions differ only in the elabora- 1980, p. 5). On the 1974 and 1976 editions of the Special Studies tion. All agree in defining a fault as a tectonic fracture* or break Zones maps, such faults, including the San Andreas, Calaveras, in the earth's crust along which displacement (horizontal, verti- Hayward and San Jacinto faults and their branches, were zoned cal, or diagonal movement) has taken place. In elaborating, unless it could be demonstrated that specific fault strands were inactive all some definitions further specify ( 1 ) that the fracture or break during of Holocene time. Because of the large num- may be either a discreet surface or a wide zone of fractures; (2) ber of potentially active faults in California, the State Geologist that the fault may be a result of repeated displacements which adopted additional definitions and criteria in an effort to limit took place suddenly or very slowly as a result of creep slippage; zoning to only those faults with a relatively "high" potential for and (3) that the cumulative displacement may be measurable in surface rupture. Thus, the term "sufficiently active" was defined fractions of an inch (centimeters) or in miles (kilometers). as a fault for which there was evidence of Holocene surface The use of the designation "active fault" on a map in this displacement. This term was used in conjunction with the term country (and probably in the world) began with the publication "well-defined," which relates to the ability to locate a Holocene of the Willis and Wood "Fault map of California" (1922). Un- fault as a surface or near-surface feature. All faults zoned since fortunately, two difTerent sets of criteria were used in different 1977 have had to meet the criteria of "sufficiently active and parts of the state by the two compilers. Willis designated an well-defined" (Hart, 1980, p. 5-6). "active fault" as one on which slip is likely to occur and a "dead Another special definition is used by the U.S. Water and Pow- fault" as one on which no further movement may be expected. er Resources Services (formerly the U.S. Bureau of Reclama- His criteria for distinguishing between the two, however, were tion) in the design of dams. To this agency, any fault exhibiting quite vague and his active faults were based primarily on a relative displacement within the past 100,000 years is an active

"growing mountains" theory. Wood, who compiled the southern fault (Slemmons and McKinney, 1977, p. 19.) part of the state, was more factual and designated his "active Table 2 is a summary of the fault definitions in common use faults" as those which have shown activity in historic time, or and the factors on which they are based. Each of these definitions which have physiographic evidence of recent surface dislocation. is concerned with future fault activity and this is based on the Wood's definition of an active fault is thus based on observation recent history of the fault. Depending on the type of structure and has survived through the years with only slight modification. being planned and the acceptable risk to be taken, the definition

The main changes to Wood's definition have been: ( 1 ) the addi- of an active fault may be based on the last 1 1,000 to 100,000 tion of other criteria, principally seismic, for identifying active years or on repeated movements during the past 500,0(X) years. faults, and (2) the addition of a spsecific time frame since the last The recent history of movement on a fault can be determined by fault movement for separating "active" from "inactive" faults use of geological or historical criteria. A summation of these (possible because of the modem capability of deteriming the criteria is presented in Table 3. time of movement on them). Of recent concern is the possibility that faults, even geological-

All definitions of "active faults" in common use imply future ly ancient ones (that is, pre-Quatemary), can be reactivated by movement commonly constituting a geologic hazard. In recent the influences of man. For example, there are now several au- years, specialized definitions vary according to the type of struc- thenticated cases showing that the filling of a reservoir can in- ture to be built in the vicinity of a fault and the degree of risk duce fault activity and earthquakes of significant size. In this acceptable for a particular type of structure. The most conserva- way, what may have been considered "inactive faults" can tive definition is that of the U.S. Nuclear Regulatory Commis- become "active faults." sion (NRC, formerly U.S. Atomic Energy Commission). In The term "active fault" is best avoided altogether when seis- defining fault activity for its special uses, the NRC sought to mic risk is not a consideration. For simply describing the charac- avoid the misunderstanding that might arise from its use of the teristics of faults, such terms as "historic fault," "Holocene term "active" by using the term "capable" in its place. A "capa- fault," "Quaternary fault," "pre-Quaternary fault," or "seismi- ble fault" is defined as a fault that exhibits one or more of the cally active fault" are preferable. With these designations, a following characteristics: ( 1 ) movement at or near the ground project geologist, after confirming the designation of a fault, can surface at least once within the past 35,000 years, or movement then go on and make his own determination of its activity rela- of a recurring nature within the past 500,000 years; (2) mac- tive to the type of structure to be built and the acceptable risk. roseismicity instrumentally determined with records of sufficient precision to demonstrate a direct relationship with the fault; (3) Historic Faults, Earthquakes, and Creep a structural relation to a fault deemed "capable" such that move- ment on one can be reasonably expected to be accompanied by which during historic movement on the other. Faults along displacement has occurred time are shown in red on the Fault Map of California. A fault In California, special definitions for active faults were devised was classified as historic if it had ( ) a recorded earthquake with to implement the Alquist-Priolo Special Studies Zones Act of 1 surface rupture. (2) recorded fault creep, or (3) displaced sur- 1972, which regulates development and construction in order to vey lines. A fourth criterion was considered, namely seismicity, avoid the hazard of surface fault rupture. The State Mining and but this was ultimately rejected for the 1975 map (for reasons Geology Board established Policies and Criteria in accordance explained in a later section). with the Act. They defined an "active fault" as one which has "had surface displacement within Holocene time (about the last 11,000 years)" (Hart, 1980, p. 21 ). The State Geologist, who has Earthquakes With Surface Rupture the responsibility under the Alquist-Priolo Act to delineate spe- cial studies zones (i.e., regulatory zones) to encompass poten- The historic record of earthquakes in California goes back tially hazardous faults, has adopted additional definitions based slightly more than 200 years to the Portola expedition of 1769, on wording in the Act. A "potentially active fault" was defined when violent earthquakes were felt in the Los Angeles region and a-s any fault that "showed evidence of surface displacement dur- recorded in the diaries of these explorers. However, no record of

•A Irctuuc (ractuir it dulinKuutublr from nontpclonic fraclum »uch us %ul«idcncc rruclur<^. IuiuUIkIc (riKluro^. el cx-lcra, by huviiiK ili ongin

Table 2. Comparison of various commonly used fault definitions. 18 DIVISION OF MINES AND GEOLOGY BULL. 201

ground displacemeni was reported by ihe expedition for this to be the site, but closer scrutiny suggests that the fault features event, although the intensity of the quake at their camp was along the Big Pme fault are probably not of historic origin. considerable. Ground rupture associated with the 1966 Truckee earthquake As far as can be ascertained, the first record of ground dis- in the Boca Reservoir area north of Lake Tahoe, is not complete- placement in California was associated with the Hayward fault ly understood. The area is dominated by northwest-trending during the earthquake of 1836. 30 subsequent earthquake About faults, but the concentration of ground breakage resulting from events occurred in California that have well-documented have this earthquake was along a northeasterly trending zone 16 kilo- ground breakage. These events are listed in Table 4, Part A, and meters long. This suggests that it may be related to a subsurface 4 California. are shown on Figure and the Fault Map of northeast-trending fault (Kachadoorian and others, 1967). During the l''52 Arvin-Tehachapi earthquake, many wide- Whether the surface earthquake effects mapped on and adjacent spread and well-defined surface breaks or cracks developed to this probable fault were due to tectonic movement or to which were noi part of the causative White Wolf fault. These ground shaking could not be determined (Carter, 1966). ground breaks were the result of ground failures during the The San Jacinto fault is one of the most seismically active shaking of this event. Because of the extensive distribution and faults in southern California. The fault has a record of historic possible significance of the cracks to future land-use planning, fault displacement along its southernmost portion; for example, some of these breaks are shown on the Fault Map. Likewise, breaks were associated with the 1968 Borrego Mountain earth- small breaks were associated with the 1971 San Fernando earth- quake and a 1934 earthquake in the Colorado River Delta area quake that were probably due to severe ground shaking. Some of Baja California. However, no verified fault displacements of these breaks also have been shown on the map. have occurred on its northern section although numerous earth- It should be noted that the dates of the earthquakes associated quakes have been associated with it. Some reports of ground with fault rupture are indicated on the Fault Map of California breakage on the northern part of the San Jacinto fault during an in red. Red triangles are placed along the historic faults to indi- 1899 earthquake were published by Danes (1907), in an Austri- cate the terminating points of observed surface displacement. an geological publication, but these reported ruptures could have Most of these points are well established, but unfortunately, the been caused by landsliding (Allen and others, 1965, p. 767; records are not always good enough to know for certain what the Sharp, 1972). extremities were in the case of several earlier earthquakes having ground ruptures. Today, when an earthquake occurs, numerous geologists and seismologists swarm into the area to study and Recorded Fault Creep map the effects, but before 1906 the relation between faulting and earthquakes was not recognized and little or no attempt was made by early-day scientists to record such data. For example, Fault creep is described as slow ground displacement usually Josiah Whitney, the State Geologist of California, was the first occurring without accompanying earthquakes. It was first recog- on the Vista fault, in oilfield Taft, California scientist on the scene after the great 1 872 Owens Valley earth- nized Buena an near quake, but he made no effort to record the ground ruptures. (Koch, 1932). It was later recognized on the San Andreas fault

Hence the full extent of these ruptures is still imperfectly known. at a winery south of Hollister, (Steinbrugge and Zacher, 1960),

What is known has been learned by modem interpretive tech- and since then has been found on several other faults in Califor- niques. The 1872 scarps at the few populated areas where the nia. It is apparently a relatively rare phenomenon outside of ground ruptures are well known (because of reports of associat- California. Creep may have preceded the 1959 Montana earth- ed damage) were observed, and low sun angle aerial photo- quake (Myers and Hamilton, 1964). Outside the United States graphs were scrutinized closely to distinguish scarps with it has only been reported in Turkey. On the Fault Map of Cali- features characteristic of the known 1872 scarps from older, fornia, fault creep has been used as the sole criterion for classify- more eroded scarps in the area. ing the six following faults as having activity during historic time: Concord, Antioch, Kern Front, Casa Loma, Buena Vista, The extent of the ground rupture associated with the 1857 and Mesa (see Table 4, Part C). earthquake on the San Andreas fault poses still another problem. In this case, the accounts of rupture were based on newspaper Fault creep of tectonic origin is often difficult to distinguish reports made by untrained observers. Thus the southern end of from nontectonic ground displacement resulting from ground- the break is reported in two different places, one near San Ber- water or oil withdrawal. In fact, creep on the Buena Vista fault, nardino and the other in the Colorado Desert. A study of the as well as on the Kem Front fault, is today generally attributed relative youthfulness of fault features on the San Andreas, many to withdrawal of oil. Creep on the Casa Loma fault is considered of which are still preserved in this semi-arid climate of southern by some to be a result of ground-water withdrawal. The creep California, suggests that the southern extent of the 1857 event shown on the Mesa fault is questionable, and there are now was at Cajon Pass and that the fault features traceable into the indications that earlier reports of creep may have been in error. Colorado Desert should be attributed to some earlier pre-historic The places where fault creep has been observed and recorded are

event. The northern extent of the 1857 rupture is also in doubt shown on the map with red dots on the fault. These locations

because of vague reports. Attempts to reinterpret its northern include both tectonic and nontectonic creep. limit have not been successful because of subsequent earthquakes Fault creep has been noted on some faults in areas where the and fault breaks in the same region. ground has been previously broken by historic earthquakes (for

There is great uncertainity about the location of the 1852 example, on segments of the San Andreas, Hayward. Coyote earthquake ruptures in southern California. Newspaper ac- Creek, and Imperial faults). But fault creep has also been ob- counts of this event describe the occurrence in a sparsely inhabit- served on other segments of active faults that have had no record ed Lockwood Valley, but because there are two Lockwood of earthquake ground ruptures during historic time (for exam- Valleys in the state that are astride major fault zones (the Big ple, certain parts of the San Andreas and Calaveras faults). Pine fault and the Rinconada fault), there is considerable uncer- Since 1975, when the Fault Map of California was published, tainty about which remote area suffered the reported 30 miles of fault creep in places on the Imperial fault has been rcpi>rtcd ground breakage. Until recently, the Big Pine fault was believed (Gilman and others, 1977). A segment of the Brawley fault (not 1985 TEXT TO ACCOMPANY THE FAULT AND GEOLOGIC MAPS OF CALIFORNIA 19

Uxahofi 20 DIVISION OF MINES AND GEOLOGY BULL. 201

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to °2 a Q. o> ?2 1985 TEXT TO ACCOMPANY THE FAULT AND GEOLOGIC MAPS OF CALIFORNIA 21

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Table 4, Part B. Historic surface faulting associated with earthquakes in Nevada and Baja California.

Earthquake 1984 TEXT TO ACCOMPANY THE FAULT AND GEOLOGIC MAPS OF CALIFORNIA 23

Table 4, Part D. Triggered creep along faults 24 DIVISION OF MINES AND GEOLOGY BULL. 201

between the epicenter locations of earthquakes and a specific Identification fault. Both macroseismic and microseismic activity were consid- ered, and all types of events were evaluated — whether they were Quaternary faults are recognized by various criteria. Because repealed earthquakes over a period of years, aftershocks of a some of the evidence becomes destroyed with time and is not larger event, or microcarthquakes detected by extensive continu- always clearly recognizable, geologists try to utilize as many bits ous monitoring by close seismic survey networks. The guiding of evidence as they can accumulate in their interpretation. Some factor was w hether or not an alignment of epicenters appeared of the most commonly used criteria include the following: to be clearly related to a specific fault. This criterion was used (1) Scarps in alluvium, terraces, or other Quaternary most sparingly because of imprecise location of epicenters (espe- units; cially with older data). In this way several faults thai otherwise (2) Lateral offsets in Quaternary units; had no observable historic surface fault displacement were tenta- (3) Stream courses offset in a systematic direction; tively classified with the group of historic faults. These included of fault-caused depressions, such as sag the Newport-Inglewood, Palos Verdes, Mendocino, Sargent, (4) Alignment ponds, fault troughs, and fault saddles; Mission Creek. Palo Colorado-San Gregorio faults, the northern that part of the San Jacinto fault, and the southern part of the Healds- (5) Markedly linear and steep mountain fronts ap- pear to be associated with a bordering concealed fault burg fault. However, because of disagreement among seismolo- gists about the significance of micn>earthquake alignments, and trace; because of the uncertainties involved with ascertaining align- (6) Ground-water barriers in Quaternary sediments ments among the random distribution of macrocarthquakes, a caused by faults (such barriers may be evidenced by decision was made not to include seismicity with the other wide- vegetation contrasts, alignment of springs and seeps, or by well data tables at ly recognized geologic and historic criteria used in making this showing comparable water different levels). official fault map of the state. The uncertainty of relating individual macrocarthquakes (magnitude 3 or greater) to specific faults in cases where there Problems is no ground displacement is well known among seismologists, although sometimes overlooked by geologists. The problem lies Using the above criteria, numerous faults can be shown to with the accuracy of epicenter locations. "Without a group of have Quaternary activity; however, as with any classification, several good stations, velocities and crustal structures are uncer- there are situations where it is difficult to decide whether to tain and location of epicenters is unreliable" (Richter, 1958, p. designate the fault movement as being Quaternary in age. 315). Well-recorded earthquakes may be located accurately within In northeastern California, for example, a large group of faults 5 km. (3 mi.), but most epicenter maps include locations with within Quaternary volcanic rocks have been shown as orange far less accuracy. Also, there are instances in which well-located lines on the Fault Map. However, in the same area and on the earthquakes do not line up with known faults. same trend, many other faults that occur wholly within some- In recent years, the sensitivity of seismograph networks has what older volcanic units have been shown as black lines. These been greatly increased. As a result, a remarkably close relation faults may have formed at the same time as those faults in the between microseismicity (magnitudes less than 3) and specific Quaternary units, but without further evidence they cannot be faults in certain parts of the state has been confirmed. Figure 5 classified as Quaternary. The faults in this area were largely shows how a section of the San Andreas fault, and the Hay ward, determined by photo interpretation and only a limited amount Calaveras and Rodgers-Creek faults are clearly outlined by the of field checking. Further field work may reveal evidence of alignment of very small earthquakes. However, historically ac- Quaternary displacement on many of these faults in the older tive faults may for periods of time show no microseismic activity; rocks. thus, a lack of microearthquakes is not conclusive evidence that In various parts of California extensive nonmarine deposits a fault is dead. For example, north of San Francisco, where a were laid down over a long period of time ranging from late long stretch of the San Andreas fault ruptured in 1906, no recog- Pliocene well into the Pleistocene. These Plio-Pleistocene depos- nizable microseismicity or macroseismicity has occurred since its (such as the Paso Robles and Santa Clara Formations in the 1906. central Coast Ranges) generally lack fossils, so the Pliocene portion of the rocks can rarely be separated from the Pleistocene rocks. Where these beds are cut by faults, geologists cannot readily determine whether the faults were active during Pliocene or Pleistocene time. A decision therefore had to he made by the Quaternary Faults compiler as to whether they should be designated as Quaternary. In order to avoid overlooking possible Quaternary faults, it was

A Quaternary fault is any fault that shows evidence of having decided to include these faults within the Quaternary category. been active during approximately the last two million years. The For dating the faults shown on the Fault Map of California, Quaternary period therefore encompasses those historic faults the Quaternary rocks depicted on the new State Geologic Map just described in the previous section. The Fault Map of Califor- were used as a guide. Although some of these age designations nia, however, treats the two terms as mutually exclusive time are probably incorrect, they were the most useful guide we had

intervals; that is, a Quaternary fault is any fault not considered at the time. Even if the rocks shown as Pleistocene are somewhat an histonc fault \\\d\ shows evidence of having been active during older—that is. Pliocene— faults cutting such rocks could be post- approximately the last two million years. Quaternary faults are Pliocene, nonetheless. In fact, if the rocks cut by a fault are /art- indicated by orange lines; historic faults, as we have seen, are Pliocene in age, then the fault is most likely Quaternary. indicated by red lines. Some dotted faults are shown as being Quaternary in volcanic Faults designated by heavy black linc-s are those without terrain such as at Mount Shasta and in Owens Valley where rcfo^«;ir«/ Quaternary displacement; faults in this category are there are alignments of Quaternary volcanic cones. These con- discussed later in the section entitled "Pre-Quaternary faults." cealed "faults" may actually be fissures or fractures along which 1985 TEXT TO ACCOMPANY THE FAULT AND GEOLOGIC MAPS OF CALIFORNIA 25

40* 0.00' "T 1 1 T

SACRAMENTO

SYMBOL 26 DIVISION OF MINES AND GEOLOGY BULL. 201

lava was extruded, and may in themselves have little or no widely accepted. However, because three million years was the displacement. But because these volcanic rocks are Quaternary accepted age for the Quaternary period while some of the State in age and occur in an area where known Quaternary fault Atlas sheets were being compiled, certain volcanic rocks of that structures exist, these structures are interpreted to be of early age (determined radiometrically) were classified as Quaternary. Quaternary age also. Some faults within these volcanic rocks could thus be older than Faults that were determined solely on the basis of geophysical the age implied on the Fault Map of California. interpretations have been used, but with caution. The same is Quaternary faults located on the basis of well-log data. true of Major Quaternary Faults The quality of the logs and the well spacing were critical factors that were considered. With geophysical interpretations (espe- Quaternary faults are abundant and widespread in California. cially those made by geologists), the date of the survey and the Many are short minor breaks, but others consist of numerous experience of the interpreters were considered, and consultation small segments that define major structural trends. Some Qua- with Rcxlger Chapman, the Division's geophysicist, was sought ternary faults are extensive, but are largely concealed under deciding w hethcr to use certain fault interpretations based before alluvium. In order to emphasize the major Quaternary faults or geophysical data. on fault zones, a pale orange band has been superimposed on the In cases where a geologic map indicates a fault separating map portrayal of the fault. Certain criteria were used to decide alluvium, especially along a mountain front, it is bedr(xk from which Quaternary faults should be selected for such emphasis. difTicult determine what age the geologist considered the often to To be considered "major," a Quaternary fault had to be charac- to be. Sometimes the map's scale is such thai it cannot show fault terized by one or more of these factors: a fault or fault zone in bedrock close to the alluvium contact. Sometimes, when a mapper interprets a mountain front as an (1) The fault is of considerable length (for example, usu- eroded fault-line scarp, the geologist may not be particularly ally more than 30 miles [48 km]). concerned about the age of the fault he is depicting and simply neglect to show it as a dotted line in the alluvium paralleling the (2) The fault is associated with an alignment of numerous mountain front. If such a fault is not discussed in the text, it is earthquake epicenters (such as with the Sargent and impossible to know whether it was considered to be a young or Newport-Inglewood faults). an old feature. This problem most commonly occurs in the Basin and Range and Mojave Desert provinces. In compiling the Fault (3) The fault trace is continuous with segments that have Valley Map of California, if a bedrock-alluvium fault relationship was historic displacement (for example, the Green not clear from the source data, the fault was usually shown in fault), black —not to indicate that the fault movement was necessarily (4) The fault is associated with youthful major mountain pre-Quaternary, but that the age of movement was undeter- scarps or mountain ranges (for example. Surprise Val- mined. ley, Honey Lake, and Panamint Valley faults). In many cases, it is difficult to recognize Quaternary displace- ment along a fault when the fault lies wholly within rocks older (5) The fault is associated with strong geophysical anomal- than Quaternary. This is especially true in areas of great rainfall ies (for example, the Likely, Surprise Valley, San Cle- where subtle geomorphic evidence is easily destroyed or covered mente, and Mendocino faults). by vegetation. Also, some faults have been designated by geolo- gists as Quaternary solely on the basis of photo-interpretation of Certain faults near the California-Nevada border that are suspected geomorphic features. Later field investigation, includ- shown as major Quaternary faults appear to be short. These ing trenching, may disprove the Quaternary designation or, in faults, however, continue for many miles into Nevada and are, some cases, the existence of a fault. therefore, major structural features. Some faults that may actually have been active in historic time As with any classification, cases arose where the data were not are shown as Quaternary because the activity went unobserved clear-cut, and it was necessary to decide somewhat arbitrarily or unrecorded. It is not surprising that such activity on faults whether to include a fault as major. In general, the policy was located in sparsely populated, remote areas such as in the deserts to keep the number of emphasized faults to a minimum. If one or in the heavily forested mountains would go unnoticed or, if were to extrapolate segments of faults across greater distances, noticed, never be recorded. many more Quaternary faults could be shown as major, but the writer preferred to await additional information in such cases. Plio-Pleistocene Boundary Controversy

The duration of the Quaternary period is not well defined, and Philisophy of Conservatism the position of the Pliocene-Pleistocene time boundary in Cali- fornia has been considered at different places by various experts In general, a "philosophy of conservatism" was followed in in recent years. The Pliocene-Pleistocene boundary is generally depicting the c.v/cvj/ of Quaternary faulting; that is, where local based on palcontological concepts and the first evolutionary ap- evidence indicated that a fault has had displacement during pearance of certain species (Handy and Wilcoxon, 1970, p. Quaternary time, the entire length of the fault was shown as 2939). The palcontological evidence is correlated to magnetic Quaternary unless contrary evidence indicated otherwise. This events, paleo-climatic cycles, glacial events, and radiometric age "philosophy," which has also been expressed by the VS. Geo- determinations. Because of worldwide problems in correlation logical Survey (Wentworth, Ziony, and Buchanan, 1970, p. 4-5), and disagreements among the experts, the duration of the Qua- takes into account the desirability of calling possible geologic ternary period has been variously reported as being from one problems to the attention of decision-makers fK'fore critical million to three million years. The longer lime interval has now structures are built. If possible problems are known, they can be been largely discredited (Bandy, 1969, also Handy and Wilcox- investigated, and their presence or absence be established, so that on, 1970, p. 2939), and an age closer to two million years is more appropriate modifications of plans can be made in advance of 1985 TEXT TO ACCOMPANY THE FAULT AND GEOLOGIC MAPS OF CALIFORNIA 27

siting or before detailed design and construction. Omission of the Accuracy of Fault Locations possible geologic hazards might lead users of the map to an erroneous conclusion that none existed. The maps that were Fault traces are indicated in the same way on the Fault Map compiled by Wentworth, Ziony, and Buchanan of several coastal of California and the Geologic Map of California. The faults are areas in southern California were used in the preparation of the indicated by solid lines where the location of its trace is accurate, Fault Map of California, and in these areas their philosophy was by dashed lines where they are approximately located or in- directly incorporated. Elsewhere in the state, this conservative ferred, and by dotted lines where covered by younger rocks or philosophy was followed, but perhaps not as rigorously because concealed by lakes or bays. The fault traces are queried where of the vastly greater area covered and the less specific character their continuation or existence is uncertain. of the information available. The U.S. Geological Survey prac- The accuracy of fault locations depends on the area studied tice is to include some questionable information as long as it has and on the confidence that the geologists have in their work. A some basis and is reasonable (Wentworth and others, 1970; geologist may show a fault as solid or dashed depending on such Ziony and others, 1974). Hence, individual faults and connec- factors as how well the feature is exposed, the scale of the map, tions between faults were shown where they were considered the amount of time spent in the field, the extent of vegetative reasonable, even though conclusive evidence for their existence cover, and the complexity of the geology. With such variables, may be lacking. the degree of certainty in fault depiction varies greatly on a map On the Fault Map of California, aligned faults were generally compilation such as the Fault Map of California. However, even not connected unless the gap between was too narrow to repre- though the degree of certainty may not be uniform, the map sent adequately at the map's scale; instead, an attempt was made accurately reflects the source data (within the limits of scale) to follow the source data as closely as possible. However, because and gives the map-user an indication of the degree of certainty of an extensive review of the Fault Map by many geologists, both on the location shown for the various faults within the state. the location and the extent of Quaternary faults shown on the Thus, the map-user should be able to distinguish those faults that Fault Map were carefully considered and many modifications are well located (shown by a solid hne) from those that have were made. As a result, the 1975 Fault Map of California is the some degree of uncertainty in location or existence (shown by most complete and accurate portrayal of faults known in the dashed or queried lines) . Of course, to be more precise, a map- state at the time of publication. The data on faults of California user should refer to the larger scale maps from which the compi- are constantly being evaluated and re-evaluated and, as time lation was prepared (Appendix D). passes, new information will support or modify the Fault Map. The map-user must keep in mind three factors regarding the It is obvious, therefore, that the map should be periodically accuracy of faults portrayed on the Fault Map. First, a fault is revised and new editions pubUshed. not usually a simple, continuous feature; more often than not it is a zone or feature made up of discontinuous segments. Second- Pre-Quaternary Faults ly, geologic features are mapped in the field by "eye" as they relate to topographic and cultural features. Where a fault crosses

Pre-Quatemary faults are shown by heavy black lines on the a featureless or gently undulating region, or where the land is Fault Map of California. They are defined as faults that are older densely vegetated, the mapped fault traces may be off by signifi- than Quaternary (older than two milhon years) or faults with- cant distances. Thirdly, on the 1:750,000 scale map, the width out recognized Quaternary displacement. There may be in- of a scribed fault line (0.012 of an inch) represents in itself about

stances in which the youthfubiess of a fault is not recognized for 232 meters (760 feet). several reasons: Depiction of concealed faults poses a special problem, particu- larly for the faults in the Great Valley. Here the fault evidence (1) The fault may not affect Quaternary rocks because is taken largely from oil company maps of selected subsurface none were present or, if ever present, they have since horizons, and many of the faults shown are at great depth. If a been removed by erosion. fault is vertical, its projected surface location lies directly over the fault at depth. However, if the fault is inchned, as commonly (2) The fault may not retain evidence of youthful displace- happens, the vertical projection of the fault to the surface is not ment because such evidence has destroyed been by directly over the fault. Such projections shown on the Fault Map erosion or covered vegetation. is especially by This true can only be approximate and may indicate fault trends only. The in areas of high rainfall. main purpose of showing the faults is to indicate that the Great Valley is not an area devoid of faults. More subsurface informa- (3) The stratigraphic or geomorphic evidence may have tion would undoubtedly show that the Great Valley harbors been removed or covered by works of man, such as in many more faults than the Fault Map of Cahfomia now indi- urban areas. cates.

(4) The fault may not have been studied in sufficient detail Faults such as the San Andreas, Hayward, San Jacinto, White to ascertain when displacement last took place. Wolf, and San Fernando, which have ruptured during historic time, and the Garlock fault, so well exposed in the semi-arid Therefore, many of the faults shown as heavy black lines may desert of southern California, have all been mapped in great be young and possibly may become active. An example of this detail. These studies show that the faults occur as a series of is the Cleveland Hill fault, which ruptured in the August 1975 multiple breaks, rather than as a single continuous fracture. Oroville earthquake. Subsequent studies have shown that the Large-scale strip maps of these faults were used in our compila- fault lies within the Foothill fault system, which extends for more tion as the source data for showing more meaningfully the actual than 240 km (150 miles), but prior to the 1975 earthquake, most nature of these important California faults. geologists viewed this system as a very ancient and "seismically Offshore faults that are concealed beneath the ocean (they are dead" fault zone. Also, it must be stressed again that many faults discussed in the next section) are shown as dashed lines on the have been included with the faults designated as pre-Quatemary compiled map to indicate that their location is generally less because of a lack of age data. accurate than is the location of faults mapped on land. Such 28 DIVISION OF MINES AND GEOLOGY BULL. 201

faults are located by acoustic-reflection profiling from ship- Coast Range Thrust board, and the problems of ship position and record interpreta- tion naturally introduce certain inaccuracies. The Coast Range thrust, first described by Bailey, Blake, and Jones (1970), is depicted by open barbs. This fault rnarks the Offshore Structure upper boundary of a long-active, late Mesozoic subduction zone extending from Oregon nearly to Santa Barbara. In most cases,

the fault surface is now very steep, but locally it is flat or has been A.C. Lawson (1893) was one of the first to point out dias- folded into prominent hooks (Blake and Jones, 1977, p. 6). It trophism along the coast of southern California based on an is best exfKJsed in northern California and becomes more difficult analysis of the topography of the Channel Islands. He noted that to follow in its central and southern part because of modification the prominent marine terraces at San Pedro Hill on the mainland by later vertical and strike-slip faults or because it is concealed and on San Clemente Island do not exist on Santa Catalina by younger rocks. Island. He attributed this to submergence of Santa Catalina E.H. Bailey and other geologists of the U.S. Geological Survey Island. Later he made structural interpretations of the California at Menio Park were most helpful in identifying this structure on coastal area from bathymetric charts. He concluded that "por- the 1 :250,000 scale work sheets so that it could be more accurate- tions of the (continental) slope where the contours are crowded ly portrayed on the I .750,000 scale maps of the state. together... can scarcely be interpreted as other than fault scarps," The Coast Range thrust brings together the Mesozoic rocks and he compared them with the fault-scarp of the eastern front of the Franciscan Complex and the Mesozoic rocks of the Great of the Sierra Nevada (Lawson and others, 1908, p. 13-15). Valley sequence. The contact is easy to recognize where the One of the most detailed fault maps of the southern California ophiolitic rocks (a sequence of ultramafic rocks with mafic rocks offshore, based chiefly on sea floor topography, was made by above) that occur at the base of the Great Valley sequence are K.O. Emery (I960, p. 79). However, with modern sparker pro- in contact with the Franciscan Complex. However, if the Fran- filing, knowledge of offshore structure has increased so rapidly ciscan rocks are in fault contact with strat^i of the Great Valley that faults and also folds can be based on much more than sequence, one cannot be sure whether the contact is the Coast inferences made from the configuration of bathymetry. Unfortu- Range thrust or a later vertical or strike-slip fault. Also, if the nately, much of this new information is retained in oil company Franciscan rocks border serpentinite, which is itself not overlain exploration files and is thus unavailable, but the broader aspects by other ophiolitic rocks or strata of the Great Valley sequence, of these data are occasionally released, as for example in the one cannot be sure whether the contact is the Coast Range paper on northern and central California offshore petroleum thrust. Such stratigraphic problems made the plotting of the geology published by the American Association of Petroleum Coast Range thrust very difficult in many places. Additionally, Geologists (Hoskins and Griffiths, 1971). Most of the available the scale of the map is such that details of the pertinent stratigra- information, however, comes from recent studies and pubHca- phy do not always show. tions by the U.S. Geological Survey and various universities and These newer concepts were not used in the older mapping. In institutions, especially the University of Southern California and fact, faults on old maps were sometimes shown or omitted on the the Scripps Institute of Oceanography. basis of now-outmoded interpretations. For example, ultramafic Although the quality and quantity of data are not uniform in rocks that would be interpreted today as klippen of Great Valley the offshore area, an attempt was made to acquire all data that ophiolite were mapped with intrusive, non-faulted contacts. were available and to show at least some structural data for the The Coast Range thrust interpretation gives us an explanation entire California coastal area. Thus, for the first time, the Fault of the heretofore inexplicable juxtaposition of the two great belts Map of California depicts offshore faults (and on the Geologic of coeval Mesozoic strata: the largely chaotic and rarely fossilif- Map of California, offshore folds as well). erous Franciscan Complex; and the orderly and abundantly fos- Most of the offshore structures record late Cenozoic tectonism siliferous Great Valley sequence. The serpentinite lying which may in fact, be of Quaternary age. As incomplete as these immediately above the Coast Range thrust, previously thought data are, one is struck by the activity and mobility of the conti- to have been intruded into a fault zone, is now interpreted as part nental shelf area. By the depiction of offshore structure, one can of the Mesozoic oceanic crust on which the Great Valley se- see the continuity of such major faults as the San Andreas fault, quence was deposited. More recent work in the Coast Ranges has the Seal Cove-San Gregorio-Palo Colorado-Hosgri fault zone, expanded the concept of subducting plates into a more complex and the Newport-Inglewood-Rose Canyon fault zone as they pattern [for example, see Blake and Jones (1974) on the origin leave land and reenter at more distant points. One can also of Franciscan melanges as imbricate thrust sheets], but this work recognize the characteristic northwest-trending structural im- was done after the compilation of the 1:750,000 scale geologic print of the Coast Ranges and the Peninsular Ranges provinces and fault maps of California and hence could not be utihzed on on the adjacent continental shelf area and the west-trending these maps. structural continuation of the Transverse Ranges province off- shore. Also, a part of the anomalous west-trending Mendocino fault zone can be seen offshore. This feature actually extends westward for more than 3700 km (2300 miles) and one can Circular Fault Structures ponder the character of this structure as it impinges on the continent at Cape Mendocino. Menard (1955) pointed out that Two very interesting circular and elhptical fault structures lie this IS the only one of the several offshore fracture zones that on the east side of the Sierra Nevada, just south of Mono Lake offseus the continental slope, but the fault has no clear topo- (Figure 6). The larger of the two is the Long Valley Caldera, a graphic or fault continuation where it comes ashore at Cape 16- by 31-km ( 10- by 19-mile) elliptical depression. This feature Mendocino. has been mapped in part by surface exposures, but the connec-

Recognizing these offshore structural features is very impor- tions and complete closure have been determined from geophysi- tant because of their role in the siting of critical engineering cal studies, especially gravity surveys (Pakiser and others, facilities along the coast, and in the evaluation of offshore min- 1964). The caldera has been studied by several geologists over eral resources. the years, and has recently received many detailed geological. 1985 TEXT TO ACCOMPANY THE FAULT AND GEOLOGIC MAPS OF CALIFORNIA 29

II9°I5'

20 KM

i, - 37°45'

- 37° 30

MODIFIED FROM BAILEY, AND OTnERS, i976 ii8°45' il8°30' ,8°I5'

Figure 6. Generalized map of the Long Valley-Mono Craters area showing location of faults.

geophysical, and geochemical investigations as a result of a geo- Future Changes in Fault Depiction thennal study program. According to Bailey and others (1976),

the Long Valley structure is a volcanic caldera left by the erup- Most of the geologic maps that were used in compiling the tion of the Bishop Tuff some 0.7 million years ago. As a result, Fault and Geologic Maps of California probably show only a the Long Valley magma was partially emptied, and its roof small fraction of the faults that actually exist in the area of the collapsed along arcuate ring faults. maps. This is illustrated dramatically in mine mapping where The Mono Craters, to the north, between Long Valley and many more faults are commonly visible in underground work- Mono Lake, are another ring-fracture zone of nearly circular mgs than are apparent at the surface. On older maps, faults of

configuration. It is even younger (Holocene) than the Long small displacement have often been ignored and dismissed as

Valley caldera. However, according to Kistler ( 1966), the arcu- merely local features of little significance in the tectonics of the

ate fault trace of the Mono Craters is probably the protoclastic area. While it may be true that such features have had little effect border of a quartz monzonite pluton. on past geologic history, such faults, especially in young rocks. 30 DIVISION OF MINES AND GEOLOGY BULL. 201

might be harbingers of a developing stress system and could Further consideration of the Fault Map of California suggests provide important clues to future tectonic activity. In recent certain unfaulted areas, such as the Great Valley and Sierra years, much more attention is being paid to subtle geomorphic Nevada provinces. This is partly misleading. Intensive explora- features that may be evidence of Quaternary faulting. Thus, tion in the oil and gas fields of the Great Valley has revealed that inconspicuous geomorphic features in the topography of valley numerous faults lie within the sedimentary strata of the valley alluvium, like those along the pre-earthquake San Fernando at various horizons, indicating faulting at different times in the fault, will hopefully be detected and allowed for in planning past. It is also suspected that extensive faults exist in the base- decisions. ment rocks underlying the Great Valley. The Sierra Nevada, prin- Active faults and earthquakes are now the subject of intensive cipally a huge batholith consisting largely of ancient multiple research which will improve the interpretations shown on the intrusions, however, is apparently devoid of large faults except Fault Map of California. Since its publication in 1975, many new in two places. The first place is near its southern margin, where data have been collected, and future detailed fault studies will the Kern Canyon fault lies exposed in granitic rocks and is require many changes on the Fault Map. Thus, the length or prominently emphasized in places by Pleistocene glaciation. The location of certain faults will be modified, and the class of activ- second place is at the western margin of the batholith where the ity for some faults will be changed. Some faults that are now Foothills fault system lies in old, pre-batholith rocks. The well- shown as pre-Quatemary (or age unknown) will be changed to developed faults in the pre-batholith rocks suggest that the site Quaternary as evidence for Quaternary movement is discovered. of the batholith was earlier extensively faulted, perhaps forming

It is less likely that faults now shown as having affected Quater- a weak area in the earth's crust that the magma could easily nary rocks will be changed by further studies unless the age of invade during Mesozoic time. the rocks was originally misinterpreted. It is also expected that additional mapping will reveal new, as yet unsuspected faults of both Quaternary and pre-Quatemary ages. Mapping tools being Structural Provinces used widely today that only a few years ago were seldom utilized in fault evaluation —for example, trenching, boreholes, detailed An analysis of the structural features of the state reveals cer- geomorphological studies, and radiometric age determinations tain trends and patterns which appear to define structuraJ prov- —are continually providing new data. inces* and specific blocks. Each structural province is Hopefully, future work will be able to determine the age of characterized by faults of a predominant trend or pattern, or in faults more accurately within the Quaternary period, so that some cases, by two or more intersecting trends. Folds within those faults that have affected rocks of the late Quaternary or these structural provinces are similarly related, and together, Holocene epoch can be shown separately. A better knowledge of faults and folds are the result of stresses acting on and within where faulting has occurred within the most recent geologic past each block in each province. As will be shown, an understanding should be helpful in inferring what is likely to happen in the of the distribution and nature of Quaternary faults in California future. Thus, succeeding editions of the Fault Map of California should be a clue in the understanding of present stress fields. should attempt to distinguish those faults with recognized Holo- No attempt will be made in this paper to analyze these stress cene movement, as well as Quaternary and historic designations. fields. Such analysis requires an understanding of the structural The Fault Map of California, 1975 edition, is a provisional blocks which respond as units to any applied stresses and the inventory of faults in the state, which should be revised periodi- effort here is to recognize and describe the component blocks. being cally to keep abreast of the vast amount of new data Each of the crustal blocks is of irregular shape and interacts generated. Such information is vital to geologists, seismologists, with neighboring blocks in a complex fashion, much more com- engineers, planners, and others who use these data in their work. plicated than the model envisioned for the conventional stress ellipsoid type of analysis. Furthermore, the blocks are highly fractured internally and thus are not homogeneous. Nonetheless, FAULT PATTERNS an understanding of the stresses on each individual block would be helpful in predicting where and to what extent future fault The Fault Map of California depicts many fault types and ruptures and earthquakes might take place. An understanding of many major and minor faults. On close analysis, a characteristic the distribution and nature of Quaternary faults in California is orientation of fault traces over large segments of the state is one clue in the understanding of present day stress fields. apparent. Some faults stand out because of their great length, or As a result of some 140 years of geologic mapping in Califor- because they separate vastly different rock types (as is apparent nia, we now have much empirical data about the geologic effects on the companion Geologic Map of California), or bound or of the stress in most parts of the state as recorded in the rocks terminate major mountain ranges. The San Andreas fault is in the form of faults and folds. Because California has had a long considered the master fault in California, and is now recognized and changing structural history since Precambrian time, and as one of the major faults in the world, separating two of the because so many of the structures revealed in the rocks are a earth's major plates. Conjugate to the San Andreas are the Gar- reflection of long-sin;e departed or reoriented stress fields, focus

lock fault and its probable offset western counterpart, the Big is here made on the most recent sequence of events and on the Pine fault. The Big Pine fault, together with the prominent Santa patterns of faults within the provinces and blocks that are de- Ynez fault and the Malibu-Santa Monica-Raymond Hill faults, fined largely by major Quaternary structures. Some of these form part of the boundaries of the east-trending Transverse structural boundaries are covered by alluvium or young rocks,

Ranges province in southern California. The Sierra Nevada-Ow- and so sometimes it will be necessary to consider earlier struc- ens Valley fault zone defines a north-trending zone and, unlike tural patterns that may control later patterns. In some parts of the earlier described strike-slip faults, is the most conspicuous the state, boundaries are not well defined because of incomplete normal fault zone in the state and perhaps in the western Cordill- geologic mapping; in these isolated cases, the boundaries sug- era gested may need later modification.

"Dwae itnjctural province* ihoujd not be cxmfujed with the geomophic provinces by which the state ij often described. Some of the structural province boundaries coincide with the Seoniorphic provinces, but others do not 1985 TEXT TO ACCOMPANY THE FAULT AND GEOLOGIC MAPS OF CALIFORNIA 31

Interaction between and among the blocks has caused second- Peninsular Ranges Block ary stresses within individual blocks. The internal shearing and

rupturing caused by these stresses have resulted in the formation The caslcrn boundary of the Peninsular Ranges block is de- of many sub-blocks. Thus, the crust of California is comprised fined by the Dillon fault, which closely parallels the San Andreas of several structural provinces which form a mosaic of blocks fault zone, and its .southeast projection through the Orocopia

and sub-blocks of varying sizes and shapes interacting in a com- and Chocolate Mountains (fault 1 A on Plate 2 A). This fault also plex fashion. marks a separation between the prominent northwest trending Various geologists have noted fault patterns and structural faults of the Peninsular Ranges block and either the east-trend- blocks in different parts of California. For example, Cummings ing faults m the Pinto Mountains sub-block (II,) or the diverse (1976) and Garfunkel (1974) discussed the pattern of Cenozoic pattern of faults in the Sonoran Desert block (V). The western faults in the Mojave Desert block, and Wright (1976) discussed boundary continues offshore, probably as far as the Santa Rosa- the late Cenozoic fault patterns and stress fields in the Great Cortes Ridge. The southern boundary lies in Baja California. Basin. In this Bulletin, however, the writer points out fault pat- terns and blocks throughout the state.

In this discussion, the state is divided into eight structural provinces, containing 16 blocks and 24 sub-blocks, which are Major Structural Block Having defined on the basis either of predominant fault trends or of the Predominantly East-Trending Faults characteristics of faults they contain. The reader is asked to refer to Plate 2 as the following structural blocks and sub-blocks in California are defined and discussed. Transverse Ranges Block

A predominant east-trend or transverse fault trend is charac- Predominant Fault Trends Defining teristic of Structural Block II. This block is composed of the Santa Ynez, the San Gabriel, the Banning, the San Bernardino, Structural Provinces and the Pinto Mountains sub-blocks. All the major faults within these sub-blocks are left lateral and/or reverse faults. The Quaternary faults in California can be grouped into spe- cific structural provinces according to the predominant trend of the faults. Four of these provinces seem to be limited to specific Santa Ynez and San Gabriel Sub-Blocks areas with rather definite boundaries, while four additional The Santa Ynez sub-block is bounded sharply on the structural provinces are bounded by somewhat less definite (11,) south by the Santa Monica-Raymond Hill fault zone and on the boundaries, and contain within them complex or multiple fault north by the Big Pine fault and its westward projection. The San trends rather than a single dominant fault trend. The first four Gabriel sub-block is bounded by the the structural provinces are subdivided into a number of blocks and (11,) San Andreas, Cucamonga, and the San Gabriel-Sierra Madre faults. The Santa many of these can be further subdivided by subpeirallel bounda- and the San Gabriel sub-blocks very abruptly terminate the ries into elongate slices or sub-blocks. Ynez northwest-trending faults of the Peninsular Ranges block and those in the southernmost part of the Coast Ranges block.

Major Structural Blocks With Banning Sub-Block Predominantly Northwest Faults The wedge-shaped Banning sub-block (IL) is enclosed by parts of the San Andreas, the San Jacinto, and the Banning The Coast Ranges block (la) and the Peninsular Ranges faults. Both the east-trending Cucamonga and the Pinto Moun- block (lb) (as well as their component sub-blocks) comprise tains faults abruptly terminate against this sub-block. Structural Province I, which is characterized by faults with a strong northwest orientation exemplified by the trend of the San Andreas fault. These faults interestingly, all display right lateral San Bernardino Sub-Block slip (usually with a vertical component). These northwest- The San Bernardino sub-block and the Pinto Mountains trending faults and blocks, however, are interrupted in the south- (IL) sub-block (II,) appear to be offset right laterally from sub- em part of the state by faults having a strong eastward trend or blocks 11; and II, by the San Andreas fault zone. The San Bernar- transverse direction, which define Structural Province II. dino sub-block is bounded on the north by an east-trending thrust fault, on the west by the San Andreas fault, and on the Coast Ranges Block south by the Pinto Mountains fault. The eastern side of this sub-block is not well defined by any mapped fault but is mark- ed by the termination of the San Bernardino Mountains. The eastern boundary of the Coast Ranges block lies beneath Cummings (1976) included this sub-block with his Mojave the alluvium of the Great Valley, and the western boundary is Desert block, but its internal transverse structure could exclude concealed by the waters of the Pacific Ocean. In the northern it from the Mojave Desert block, at least in recent geologic time. part of the Coast Ranges block where the east-trending Mendo- cino fault aligns with the Eel River basin, the relationships ap- pear to be very complex and may form a small intervening block. Pinto Mountains Sub-Block However, everywhere else the Coast Ranges block is dominated by a strong northwesterly structural pattern. The southern The Pinto Mountains sub-block (II,) is bounded by the east- boundary of the Coast Ranges block is abruptly terminated by the trending left-lateral Pinto Mountain and Chiriaco faults. Mid-

Big Pine fault and by the transverse Structural Province II. way between these faults lies another left-lateral fault, the Blue 32 DIVISION OF MINES AND GEOLOGY BULL. 201

Cut fault, which may be considered as further subdividing the Valley-Bishop area, are numerous and trend almost always Pinto Mountains sub-block (Plate 2 A). The Dillon fault clearly north. In addition, these faults align with the long north-trend- forms the western boundary. The southern boundary may extend ing zone of active faults in Nevada which extends from Owens farther south toward the ChiKolate Mountains where certain Valley into Nevada through Cedar Valley, Fairview Peak, and east-trending faults are known. However, this area has not been Dixie Valley. mapped in detail, so the southern and soulheastern boundaries arc not precisely defined. Panamint and Death Valley Blocks

Major Structural Blocks Characterized By Due east of the Kern Canyon block are the Panamint and Valley blocks (IVb and IVc). They are more crudely Northeast-Trending Fault Boundaries Death defined than the other blocks of the structural provinces but are well expressed in part by the north-trending Panamint Valley The Oarlock and White Wolf faults are the two most signifi- and Death Valley fault zones. Within these blocks are numerous cant northeast-trending faults in the state and define Structural short faults which characteristically trend northwest and Province III. which consists of two blocks.* These faults are northeast. These conjugate fault directions appear much more characteristically left-lateral, but may also have a minor reverse numerous when we include the faults designated as "pre-Quater- slip component. nary or age unknown" (Figure 7); perhaps some or many of these "older" faults may also be found on closer analysis to be Block Mojave of Quaternary age. In any event, the conjugate faults within these blocks bounded by north-trending faults collectively make a The Mojave block (Ilia) has been recognized as a separate pattern with a preferred northwest and northeast orientation, entity for a long time and was discussed in some detail by Hewett with no sign of an east-trending direction. Interestingly, this area ( 1954) and several others since then. The wedge-shaped Mojave appears to be the only place in the state where this northwest- block is bounded by the Garlock and the San Andreas faults and northeast conjugate system is so well developed—a fact suggest- on the south by east-trending faults. The eastern boundary has ing that it is acting as a unit to a specific stress system. not been mapped in detail, but appears to be defined by the junction of the predominantly northwest-trending faults within the Mojave block and the diversely oriented faults in the Sonoran Desert block to the east. Within the Mojave block, northwest- trending right-lateral faults are certainly common and conspicu- ous, although the northeast portion of the block is dominated by east-trep jing faults and may be a separate sub-block as suggested by Garfunkel (1974. p. 1938).

Tehachapi Block

The Tehachapi block (Illb) is included in this report as part

of the same structural province as the Mojave block because it is bounded on two sides by northeast-trending faults—the Gar- lock and the White Wolf faults. It is mostly comprised of granitic and metamorphic rocks like the Sierra Nevada, but is offset to the southwest from the main Sierra Nevada block.

Major Structural Blocks Characterized by North-Trending Faults

The fourth fault direction in California, that gives rise to Struc-

tural Province IV, is north-trending. The most important struc-

ture of this trend is the Sierra Nevada-Owens Valley fault zone. Several subparallel major faults of this same orientation (actual- ly, slightly west of north) make up several blocks within this structural province. All these north-trending faults are normal

faults, and any lateral component of slippage is usually right lateral.

Kern Canyon Block

One of the blocks is the Kem Canyon block (IVa), which lies between the Kem Canyon fault and the Sierra Nevada-Owens

Valley fault zone Its southern end is uncertain but is possibly Figure 7. Numerous short NW ond NE conjugate toults characteristic of the

bounded by a northeastern extension of the White Wolf fault PonominI and Death Valley blocks . (thick lines = Quaternary faults,- thin

lrcnd(Plate2A). Faults within this block, especially in the Owens lines = pre-Quaternary or undated faults)

•An wiclrnt norttwait-IrmdinK fault, the Stockton fault, lies in Ihr w*»-iurf«cr beneath the Cri-at Valley, but ha-i no apparent relationship to the Quaternary tectonics discussed here 1985 TEXT TO ACCOMPANY THE FAULT AND GEOLOGIC MAPS OF CALIFORNIA 33

Warner Block places and by the faulted tcrrane of Structural Province IV. The northeastern boundary with the Modoc block was shown by Another prominent block with characteristic north-trending Durrell (1965, 1966) as a separation of an area of relatively faults is the Warner Block (IVd) in the northeastern comer of young block faulting from a more stable mass. The northwestern the state. Most prominent is the Surprise Valley fault and the boundary is a complicated and vaguely defined junction of at block-faulted Warner Range. least four blocks. Further work in this area should help to clarify the inter-relationships. This northwestern portion of the Sierra Nevada block also contains a large mass of the older, pre-bath- East Sierra Block olith rocks through which trends the well-developed fault zone of the Melones and Bear Mountain faults. At the south end, The East Sierra block (IVe) has a well-defined boundary on these faults have a prominent northwest trend; they turn due the west side formed by the main Sierra Nevada block, but only north in the central region and then swing northwest again at the a vaguely defined boundary on the east side at the Walker Lane north end. This fault zone widens northward and splits into in Nevada. This block is characterized by block-faulting with several branches. The faults were formed in pre-batholith times strike-slip shearing. but renewed activity has been noted along parts of this ancient zone of weakness (Alt and others, 1977). The Oroville earth- Cascade Block quake of August 1975, with associated ground rupture, for ex- ample, illustrates the effects of a modem stress field acting on a The Cascade block (IVQ, in the northern extremity of Cali- very old zone of crustal weakness. fornia, is the southern tip of an elongate north-trending block which continues for many miles into Oregon and Washington. Klamath Block It is principally defined by a north-trending series of volcanoes that may be controlled by deep faults or fractures along which Impinging on the northwestern end of the Sierra Nevada block these volcanoes and lavas have erupted. is Structural Province VII, the Klamath block. This structural unit is typified by numerous ancient thrust faults. No Quater- Corda Block nary faults are known within this area of resistant granitic and metamorphic rocks. Finally, offshore of northwestern California lies another block with north-trending faults. This appears to be part of the eastern Modoc Block edge of the subducting Gorda block (IVg).

Lastly, the Modoc block forms the irregular, anomalous

Structural Province VIII. It is characterized by numerous Qua- Major Structural Blocks Characterized By temary faults, most of which trend northwest, but with some conjugate faults that trend northeast, and, in one part of this Other Types Faults Of province, with some seemingly arcuate faults. The faults are largely in young volcanic rocks, but their relationship to this The state contains four other structural provinces, which are outpouring of lava is not understood. Two long and significant in general less well defined, especially by Quaternary structures, faults appear within this unit—the Likely and the Honey Lake but which nevertheless form specific areas that have their own faults. The Likely fault appears to have a right-lateral strike-sUp si>ecial characteristics. component, while the Honey Lake fault is mostly normal dip- slip. Northwest-trending fault segments line up with the Honey Sonoran Desert Block Lake fault, and they may be part of the same fault zone extending toward Oregon. This northwest trend may be a reflection of an Structural Province V forms a rather large region which is underlying stmctural province hidden beneath the Modoc lavas,

fairly well defined on the west, but extends eastward into Ne- or it may be the result of a totally new stress field. It should be vada, Arizona, and Mexico, where its boundaries have not been pointed out that only reconnaissance mapping has been accom- studied in detail. Geomorphologically, this region is considered plished in most of this area and that most of the faults were part of the Mojave and Basin Ranges geomorphic provinces, largely unrecognized as recently as 20 years ago. but structurally it appears to form a separate province—here called the Sonoran Desert block. Its eastern boundary may be defined by the Walker Lane in Nevada and Arizona, wherein lies Coast Ranges Sub-Blocks another structural province with north-trending faults. Thrust faults are known in the Sonoran Desert block, but their extent Within the Coast Ranges block, seven sub-blocks are recog- has not been determined. In fact, much of this area has only been nized. Four of these sub-blocks are well-defined and are bounded mapped by reconnaissance, and so further analysis at this time by well-known faults. The faults are parallel for the greater part

is not feasible. of their length, and are abruptly terminated at the southern end

by the Transverse Ranges block. In central California , sev- Sierra Nevada Block eral adjacent faults converge with one amother forming blocks having remarkable mirror-image symmetry.

Structural Province VI consists of the Sierra Nevada block, which has long been recognized as a major structural feature. Santa Lucia and Cabilan Sub-Blocks Certainly this large batholith forms a resistant block and serves in some places as a buttress and elsewhere as a ram on adjacent The King City-Rinconada fault separates the Santa Lucia and

blocks. Its western boundary lies beneath the Great Valley. Its the Gabilan sub-blocks ( la, and laj). The Santa Lucia sub-block eastern boundary is clearly marked by an immense scarp in some is bounded on the west by the inter-connection of the Seal Cove, .

34 DIVISION OF MINES AND GEOLOGY BULL. 201

the San Gregorio, the Sur. and the Hosgri faults, and the Gabilan the continental borderland shown on the Fault Map of Califor- sub-block is bounded on the east by the San Andreas fault. Note nia are determined to be Quaternary upon further investigation; that the Seal Cove fault converges with the San Andreas to the in any event, all these offshore faults shown are at least of late north. Likewise, a short extrapolation of the northwest-trending Tertiary age. King City fault coincides with similarly oriented faults under Monterey Bay, which in turn are aligned with a northwest- San Clemenfe and Catalina Sub-Blocks trending portion of the Santa Cruz County coastline that is probably fault controlled, and thus converges with the San Gre- The San Clemente sub-block (lb,) is well defined on the east gorio fault. To the south, both of these sub-blocks terminate by the San Clemente fault and faults lying on the same strike to against the transverse Big Pine fault and its westward extrapola- the north. The western boundary appears to lie among the faults tion. along the Santa Rosa-Cortes Ridge. The Catalina sub-block

(lb.) is bounded on the east by the Thirty Mile Bank and the San Francisco and Berkeley Sub-Blocks Catalina Island faults and on the west by the San Clemente fault

(faults 5, 5A, and 6 on Plate 2A). The San Francisco and Berkeley sub-blocks (lai and la,) are separated by the Hayward-Rtxigers Creek-Maacama fault zone. Diego The San Francisco sub-block is bounded by the San Andreas Pahs Verdes and Inglewood-San Sub-Blocks fault on the west; the Berkeley sub-block is bounded by the The Palos Verdes sub-block (lb.) is by the next Calaveras-Green Valley fault zone on the east. The Hayward bounded major northwest-trending Quaternary fault east, fault appears to converge with the Calaveras fault to the south, to the the Palos Verdes fault and its offshore extensions on strike to the south. and likewise the Calaveras fault converges with the San Andreas The Inglewood-San Diego sub-block (lb,) is defined by the fault to the south. It is interesting to note the symmetrical rela- Quaternary Newport- Inglewood-Rose Canyon fault zone on the tion between sub-blocks la, and la,, north of the San Andreas east and the Palos Verdes fault on the west. fault, and sub-blocks la, and la, south of the San Andreas fault.

Diablo and Great Valley Sub-Blocks Santa Ana, Riverside, and San Jacinto Sub -Blocks

The next sub-block to the east is the Diablo (la,), defined in The Santa Ana (lb,). Riverside (IbJ, and San Jacinto (lb,) pan by the Ortigalita fault and its extrapolation to the north. Its sub-blocks have remarkably distinct boundaries formed by the southern boundary and its boundary with the Great Valley sub- Quaternary Elsinore fault, the San Jacinto fault, and the San block (Ia») to the east, are hypothetical; they have been drawn Andreas fault on the east side of each. A possible eighth, narrow- largely on the basis of the equidistant fault spacing concept sub-block may lie east of the San Andreas, bounded by the discussed later. Dillon fault and other somewhat older faults along the south-

east-trend of the Dillon fault (fault 1 A on Plate 2A ) Stonyford Sub-Block

Lastly, the Stonyford sub-block (la,) is the anomalous Sub-Blocks Within The Modoc Block northeast comer of the Coast Ranges block. Older faults have made the breaks dividing this comer from the main block. Al- The Modoc block (VIII) in the northeast comer of the state irregularly it though the Bartlett Springs fault on the west side of this sub- is shaped, and seems to be characterized by numer- block has now been recognized as a Quaternary fault (Hearn and ous Quatemary faults. Many of these faults trend northwest- Donnelly, personal communication, 1977), the faults within the wardly, but some also strike in other directions. Mapping of this Stonyford sub-block appear to be characterized by ancient thrust area has been mostly reconnaissance, but even so, the fault pat- faults. On the basis of photo interpretation and prominent linea- terns suggest some tentative subdivisions that are shown on Plate 5. These are identified as the Alturas, Lake, ments, it appears that the Bartlett Springs fault connects with the Eagle Diamond Grogan fault farther north, which may in turn join with a promi- Mountains, and Medicine Lake sub-blocks. nent Quaternary fault offshore. Summary

Peninsular Ranges Sub-Blocks From the preceeding discussion and by consideration of the Structure Map of California (Plate 2 A), the basic concepts con- The Peninsular Ranges block, in the southern part of the state, ceming predominant fault trends and the structural provinces is readily divisible into eight sub-blocks. These eight northwest- they define may be summarized as follows: trending sub-blocks, without exception, terminate against the

Transverse Ranges block lying to the north. All the Peninsular 1. The state is divisible into eight structural provinces, each Ranges sub-blocks in California and offshore are remarkably containing faults and folds of a characteristic trend or parallel, and all extend southward into Baja, California. pattern, or, in a few cases, two dominant conjugate direc- Three of the Peninsular Ranges sub-blocks lie almost totally tions. offshore of California, and definition of their boundaries is large- ly dependent on the ofTshore geophysical work that has been 2. The structural provinces are also divisible, so that the accomplished in recent years. Although the Peninsular Ranges state appears to be broken into a complicated mosaic of sub-blocks illustrated on Plate 2A are defined by Quaternary fault blocks. faults, the boundaries are re-enforced by the patterns of the older (a) Each block appears to be acting as a unit, but also faults. It would not be surprising if additional offshore faults in interacting with adjacent blocks. 1985 TEXT TO ACCOMPANY THE FAULT AND GEOLOGIC MAPS OF CALIFORNIA 35

(b) Stresses within each block (particularly the larger faults— in fact, many of the earthquake epicenters not lying on blocks) develop secondary faults which define major faults could represent release of stress on such diagonal sub-blocks. fauhs (Plate 2D). (c) The blocks and sub-blocks appear to be best de- There are places between major parallel strike-slip faults fined in the southern part of the state where the where no diagonal fault pattern has developed—for example, rocks are well exposed and where the most detailed between the northern parts of the Elsinore and San Jacinto faults mapping has been done. The blocks in the or between the Elsinore fault and the Newport-Inglewood-Rose northernmost part of the state are less well defined; Canyon fault zone. However, an examination of the Geologic where the forest cover is most dense and the map- Map of California at these places reveals the presence of exten- ping less detailed, the block boundaries are least sive bodies of Mesozoic and older granitic and metamorphic known. rocks. These rocks probably would tend to resist such diagonal shearing and focus the release of stress along the block bounda- 3. Most of the blocks are bounded and characterized by ries. Another place where the absence of diagonal faults is espe- Quaternary faults of great linear extent. In a few major cially noticeable is in the Gabilan block, which has virtually cases, major pre-Quatemary structures define blocks no intra-block faults and which is characterized by the granitic having common structural characteristics. rocks of the Gabilan Range between the strike-slip San Andreas and King City-Rinconada faults (Figure 10). Southeast of the 4. With only a few exceptions, all Quaternary and older exposed granitic rocks of the Gabilan Range, there is also a faults and folds within a block or sub-block are confined virtual absence of faults, but the rocks here consist mostly of a to that block and never cross its boundaries, even when thin layer of late Tertiary sedimentary rocks overlying the rigid the fault or fold may cross the entire block or sub-block. granitic rocks. Here, however, gentle folds in the overlying sedi- mentary rocks, exhibit north northwest-trending axes along the 5. The most common fault trend in California is northwest direction of the expected diagonal faults. with east being secondary. Northeast-trending faults are relatively few but include two major faults—the Garlock and the White Wolf. North-trending faults are not com- mon and usually form more complex, segmented fea- EN ECHELON FAULTS tures. Within the northern Coast Ranges, the major Quaternary strike-slip faults 6. (a) All major northwest-trending Quaternary faults are which bound certain sub-blocks commonly dis- right lateral (usually with a vertical component).* play a remarkably consistent right-stepping en echelon pattern. For example, the Hayward, the the (b) All major east-trending Quaternary faults are left Rodgers Creek, Healdsburg, lateral and/or are reverse faults. and the Maacama faults each appear to be a successive right- (c) All major northeast-trending Quatenary faults are stepping continuation of a principal fault zone bounding the

left lateral and/or are re\erse faults. eastern edge of the San Francisco sub-block. And the Calaveras, (d) North-trending Quaternary faults are normal the Concord, the Green Valley, and the unnamed faults to the faults (with mostly right lateral components). north appear to be a successive right-stepping continuation of another major fault zone bounding the eastern edge of the Berke- ley sub-block. Both of these sub-blocks are characterized by diagonal shear faults. In a similar fashion, the Bartlett Springs fault lines up with right-stepping lineaments northward into FAULT COUPLES Trinity and Humboldt counties; this alignment suggests the loca- tion of heretofore unrecognized faults bounding the Stonyford An interesting observation about sub-blocks can be noted. An sub-block. apparent "couple effect" is generated in the block between two parallel strike-slip faults. In this situation, diagonal breaks occur between the bounding faults, forming a family of diagonal faults REGULARITY OF FAULT SPACING with a consistent orientation. Good examples of this can be seen in the northern Coast Ranges between the San Andreas and the The spatial geometry of the major Quaternary faults reveals Rodgers Creek-Healdsburg faults or in the Transverse Ranges another interesting relationship. This concerns their remarkable between the San Andreas and San Gabriel faults (Figures 8 and parallehsm and uniformly spaced intervals over great distances. 9). Still other examples can be seen in other parts of the state, This is particularly evident in the sub-blocks of the Coast Ranges especially in the western part where the major faults are strike- and Peninsular Ranges structural blocks. In the Coast Ranges slip. It appiears that most of the diagonal faults have no Quater- block, the spacing between the major faults bounding the sub- nary displacement and that the bounding faults do have Quater- blocks ranges from approximately 33 to 39 km along lengths of nary displacement. Perhaps this is because the diagonal faults are well over 240 kilometers (Plate 2B). Within the onshore portion activated only after a long period of time when the confining of the Peninsular Ranges block, three sub-blocks vary from 37 to stress finally exceeds the strength of the crustal materials. If so, 42 km in width (except for the southern part of the Santa Ana the stress on the diagonal faults is intermittantly accumulated block, which is as much as 72 km wide; however, there the and relieved, while the confining parallel faults undergo more southern California batholith widens to its greatest extent). Off- frequent strike-slip movement. Hence, it should not be surprising shore the spacing interval is 32 to 42 km with the Palos Verdes if an occasional stress release occurs on some of these diagonal fault appearing to divide a 32 km wide block into two sub-blocks.

' \t fir^t cLiiic*', It appears th.tt thi- fjiiiiK of ^.horl norlhwrsl-trciuliii).: Titills in iiorthrrii ( ;.iliforiii.i known .i\ Ihi- I'.iskt-nl.i. I'lldtT Ort'fk .(tut Oold l-ork f.tults. «hich diNpl.ict^ I/)\%er

( .'f c't.ic*-<>ns .ind Jnr.isMC rncks left Litcr.ill> . is .in oxcoplion to the b.isic cnncrpl prrsnili-d horr .ilxiiil iKirthwcNl Irrnilin^ f.llilts Im'iiik rinht l.it(T;il llowrxrr. if thru- f;uilts are

mtrrprotod .!_«. tear fallll\ off the (".Oiist Rani^c thriisl. where the (;oast Ranjfr thriiNt liKips arolilKl the Klani.ith Monnl.iiiis Iwfore hea{lin>< south, then these northwest faults are a special case and arc Ix'hasinK a.s tear faults of this orientation would Ix* e\jx*cted to. In addition, thes*- faults .irc \erv oUI and h.i\e no ri-coKni/ahlc Qiiaternars dis|ilacenicnt (Jones and Insin, 1971). 36 DIVISION OF MINES AND GEOLOGY BULL. 201

\ •. V c

Figure 8. Diagonal faults formed between two major strike-slip faults, the Son Andreas ond the Rodgers Creeli-Heoldsburg faults.

The major faults bounding the three adjacent north-trending faults (see Fault Map of CaUfomia) strongly suggest such a structural blocks—Kern Canyon, Panamint, and Death Valley continuation of both the strike-slip faults and the diagonal fault —also display roughly equidistant spacing. Two of these blocks system. are about 50 to 53 km wide, while the third is about 42 km wide To extend precisely the mapping of faults paralleling the San over distances of over 160 km. Andreas trend northward into the terra incognita of the northern It appears that regularity of spacing between major faults, Coast Ranges block will be difficult because of the existence of repeated in many parts of the state, must be more than a coinci- numerous and gigantic landslides. However, one thing is certain dence. It suggests that the rigidity of the earth's crust is behaving —the major faults coming up from the south must continue into in some consistent fashion related to the strength of the crustal this landslide terrane. Indeed, many of the landslides are in all or even sub-crustal materials and to the direction of deep stresses probability a reflection of the weak rock crushed by the suspect- applied to the structural blocks.* If such be the case, then the ed faults. The strong northwest-trending lineaments, expresed by existence of faults in unmapped areas (such as some offshore the major river drainages, are an indication of the structural areas) and in incompletely mapped areas (such a.s in northwest- grain of the country. Unfortunately, the river-undercutting of em and southeastern California) might be predicted by extrapo- the steep slopes in this high rainfall area, releases the landslides lation of known faults by maintaining equidistant spacing which can easily mask fault traces. between them. For example, the northwestward continuation of Twenty-five years ago, H.W. Menard (1955, p. 1172) noted the San Francisco and Berkeley sub-blocks into Mendocino the regularity of fault spacing in the tx;ean floor off California County would therefore be expected, by extension of the Maaca- and, on the basis of this regularity, predicted the existence of ma and Barilctt Spnngs faults (with right-stepping en echelon additional offshore fracture zones. "Four fracture zones have offset). The continuation of an accompanying diagonal fault been discovered," writes Menard, "and others may be found as system between these strike-slip faults would also be anticipated; more echograms become available from other regions in the and, in fact, topographic lineaments and incompletely mapp>ed Pacific." Figure 1 1 is Menard's map showing the location of

•Upon cofnpiplion of thu nianuKnpt. in which the wnlrr independently developed the ideas of equidiitani fault spacing m C^ifornia. he came upon foreign reports describing this

phmocnenon in other paru of the world Kspecially noteworthy are papen by j. Kuttna ( 1966) and Radan Kvet ( 1974} In these papers the authors describe examples of equidistant rupture lystetiu In Czechoalovalda. Austria, Scotland, and Sardinia. IPSS TEXT TO ACCOMPANY THE FAULT AND GEOLOGIC MAPS OF CALIFORNIA 37 38 DIVISION OF MINES AND GEOLOGY BULL. 201

o c E o

0"2 ^ 6 o — E ^

c — p <

E 2

c i

= 3. £ S

E g S

^ a •*- ^ OS .Q. *- "3i c n ^ O — T O) *- .5 2" Q -5 S o 2 £o ^ t-* S S o 3 C ,_ 1985 TEXT TO ACCOMPANY THE FAULT AND GEOLOGIC MAPS OF CALIFORNIA 39

these four fracture zones. Speaking of other likely fracture zones, in the block between the bounding strike-slip Menard (p. 1172) writes: faults, (b) Where diagonal faults do not develop, or are not Possible locations are about 600 miles north of the Mendo- well developed, between parallel strike-slip faults, cino fracture zone, midway between the Murray and Clar- the reason could be that resistant granitic and ion fracture zones, and about 600 miles south of the mctamorphic rocks lie at or near the surface Clipperton fracture zone. These positions are suggested by between the bounding strike-slip faults. the regular spacing of the zones. 4. Major Quaternary strike-slip faults bounding sub- The most probable position for another fracture zone is blocks in the central Coast Ranges display a consist- midway between the Murray and Clarion fracture zones. A ent right-stepping en echelon pattern. zone at this location would give a regular unit spacing for

all the zones from Mendocino to Clipperton rather than a 5. Spacing between the major parallel Quaternary faults unit spacing between the northern and southern pairs and shows a remarkably uniform interval. double the unit spacing between the middle pair. (a) In the Coast Ranges block this equidistant spacing interval in five sub-blocks ranges from 33 to 39 km over distances in excess of 240 km. As a matter of fact, later work has proved Menard's prognostica- (b) In the Peninsular Ranges block, the equidistant

tion correct. Figure 1 2 shows the configuration of the same area spacing interval ranges from 32 to 42 km in five as Menard's, but is based on much additional data collected at sub-blocks. a later date. Note how the equally-spaced faults have been dis- (c) Where spacing intervals apjjear to vary, they oc- covered. Of course, the offshore crustal blocks between Menard's cur as a multiple of, or equal fractional parts of, fracture zones are several orders of magnitude larger than the the regular interval. sub-blocks herein described for onshore parts of California. The (d) Three adjacent north-trending blocks east of the offshore blocks are merely presented here as an example of crus- Sierra Nevada block approximate equidistant tal materials undergoing stress, which deform in a more or less spacing, two being about 52 km wide and the uniform, predictable fashion. third 42 km wide. Menard also saw some possible correlation between the off- (e) Regularity in fault spacing has been noted before shore fracture zones and the geologic provinces on the conti- in offshore California areas by Menard and nents. He felt it weis particularly significant that the Great Valley served as a useful concept in correctly predicting and the Sierra Nevada, as well as other geologic provinces south the existence of additional offshore fracture of California, all appeared to be terminated at their northern and southern ends by the onshore continuation or projection of off- shore fracture zones. FAULTING AND PATTERNS OF SEISMICITY SUMMARY ON FAULT GEOMETRY

California is situated within a mobile belt of rocks on the The following facts can be stated about the geometry and boundary between the Pacific and North American plates. Here distribution of sub-blocks, fault couples, and fault-spacing regu- the rocks are highly folded as well as faulted, and in places are larity: marked by numerous volcanoes, some of which have been active in historic time. The state is also part of the well-known circum- 1. Each sub-block has remarkably parallel boundaries for Pacific earthquake belt, now recognized as coinciding with inter- great distances. connecting plate boundaries around the Pacific Ocean. As such,

it should be no surprise that California has had, and will contin- 2. (a) Each in the sub-block southern Coast Ranges ue to have, numerous earthquakes. abruptly terminates against the Transverse Ranges block. (b) Each sub-block in the northern Peninsular Relationship of Epicenters To Faults Ranges likewise abruptly terminates against the Transverse Ranges block. Various inaccuracies are inherent with epicenter maps, and (c) The northern termination of two Coast Ranges most epicenter patterns appear more or less randomly positioned sub-blocks (I,) and la,) by convergence is sym- in relation to individual faults. However, with care, some rela- metrical with the southern termination by con- tionships can be observed between faults and earthquake epicen- vergence of two other contiguous ccniral Coast ters of certain magnitudes. For example, almost all of the

Ranges sub-blocks (la, and Ijl,), that is, the Seal earthquakes of magnitude 6.0 and greater in the last 75 years Cove-San Gregorio fault converges with the San (see Plate 2C) have epicenters that are on or near major Quater- Andreas and with the projected Rinconada-King nary faults. In a few cases where this relationship does not seem City fault zone, while the Green Valley-Calaveras to exist, the epicenter locations could be suspect, for they may fault zone converges with the San Andreas and have been far from the seismic networks existing at the time. with the Rodgers Creek-Hayward fault zone. (These earlier locations are often rounded off to the nearest degree, half-degree, or quarter-degree latitude and longitude). 3. (a) Most sub-blocks bounded by strike-slip faults Two earthquake events in the magnitude 6 range that may not contain diagonal faults that may be a result of a be related to major Quaternary faults are the 1947 Manix and couple effect whereby diagonal shears are formed the 1966 Truckee earthquakes. Although the magnitude 6.2 40 DIVISION OF MINES AND GEOLOGY BULL. 201

Figure U. Fracture zones illustrated by Menard (1955).

ES MS

Figure 12. Port of a tectonic mop of the world (Condie, 1976) including the some oreo illustrated by Menard 25 years previously (compore with Figure 11). Note nearly equol spacing between Menard's faults and additional discoveries. 1985 TEXT TO ACCOMPANY THE FAULT AND GEOLOGIC MAPS OF CALIFORNIA 41

Manix earthquake is associated with the Manix fault, along Table 5. California Seismic Record for 75 Years. which ground rupture occurred for a distance of about 1 .6 km Earthquakes (one mile), the overall length of this fault is probably no greater than 14.5 km (nine miles) —hardly a major California fault. Indeed, from the aftershock distribution, which was nearly at right angles to the Manix fault, Richter (1958, p. 517-518) felt that the ground breaks observed along the Manix fault were actually the effect of the earthquake, and that the earthquake was presumably caused by subsurface movement along a buried fault as defined by the aftershock distribution. The magnitude

6.0 Truckee earthquake is also not clearly associated with a major Quaternary fault, although ground cracking in the area was aligned for about 16 km (ten miles). However, the area still is relatively poorly mapped, and may contain unrecognized faults of significance.

Earthquakes of less than magnitude 6, which of course are far more numerous, show less close correspondence with major Quaternary faults. Reasons for this less frequent relationship include: (a) inaccuracies in location of pre- 1932 epicenters, (b) inaccuracy of epicenter locations owing to the great distance from networks existing at the time, and (c) possibility that many of the smaller earthquakes may simply be minor crustal adjust- ments within the various interacting crustal blocks and sub- blocks (as described in the previous section on fault patterns p. 31), and hence are not occurring along breaks exposed at the surface. We should also keep in mind that inchned faults, such as thrust faults, do not give rise to epicenters which project vertically to the fault's surface exposure. For example, the epic- enters of the main 1971 San Fernando earthquake, and its after- shocks, plot well to the north of the trace of the inclined San Fernando fault. A study of the fault-epicenter map (Plate 2D) also reveals a certain number of major Quaternary faults without any apparent relation to earthquake epicenters. For example, in the northeast- em part of California, there are many Quaternary faults but very few epicenters. This is perhaps because the setting is an area of extensive volcanic outpourings. The extensive faulting here may have originated from a shallow, short-term cause such as local land collapse due to volcanic activity. If so, repeated movements on most of these faults would not be expected.* Many currently "quiet" faults in other parts of the state, however, are likely to be dormant or "locked" portions of active faults. For example, long segments of the San Andreas fault that broke in 1857 or in 1906 do not today have associated epicenters. We also know from other parts of the world, such as China, Japan, and the Mediterranean, where the seismic record extends over a period of several thousand years (Allen, 1975), that the 200 years of historical record and 90 years of instrumental record of California earthquakes is far from adequate for es- timating fault activity. Seismic gaps of several hundreds of years are not uncommon in the long-term records from these ancient cultures, and hence our brief California record must be used with proper caution in evaluating the potential for recurring seismici- ty on seemingly "dead" Quaternary faults.

Relationship Of Surface Rupture To Earthquake Magnitude

In general, earthquakes in Cahfomia of magnitude 6 and greater are accompanied by surface fault rupture, but there are exceptions. The data in Table 5 (1900-1974) show a one-to-one 42 DIVISION OF MINES AND GEOLOGY BULL. 201

one of the largest earthquake events observed in Cahfomia, the fault) form confining boundaries to seismic activity, with much 1872 Owens Valley earthquake, was associated with a fault hav- more activity to the east than to the west. West of the Sierra, the ing a dominantly normal (vertical) displacement history. In Great Valley is also quiet like the Sierra. addition, two very disastrous earthquakes have occurred on Few seismic events have been plotted in the northeastern part predominantly thrust type faults—the San Fernando earthquake of the state, but this apparent lack of historic epicenters may be of 1971 and the Arvin-Tehachapi earthquake of 1952. deceptive because this sparsely settled area is remote from any seismic network. Three major faults with large displacements must have had considerable Quaternary activity—the Surprise Patterns of Seismicity Valley, Honey Lake, and Likely faults. Hence, it may be delusive to conclude that the recent history of sparse seismic activity is Although earthquake epicenters occur in most parts of Cali- an indication of an aseismic area. fornia, greater concentrations do appear in certain areas or along The western tip of the Mojave wedge, bounded by the Garlock certain fault zones. For example, the west -trending Mendocino and San Andreas faults, is anomalously free of seismic events of fault zone clearly marks a boundary between an area of great magnitude 4 and greater. Only a few Quaternary faults have been seismicity on the north and a quiescent area to the south. The mapped in this area. This may be deceptive because faults could San Andreas fault for at least 180 miles (288 km) south of San easily be concealed beneath the vast blanket of alluvium in An- Francisco, and the Hayward and Calaveras branches are all well telope Valley. earth- marked by numerous epicenters; in fact, microseismic From the foregoing, it can be seen that certain major bounda- quake monitoring by the U.S. Geological Survey, with its close- ries of seismic activity appear in the state, such as along the order network in the San Francisco Bay area, shows an even Sierran front, the Mendocino fault zone, and the White Wolf- closer relationship of seismicity to these faults (Figure 5). The Walker Pass trend. These correspond to certain boundaries of San Andreas system in southern California also displays a close the structural provinces described in the section on fault pat- relationship to earthquake epicenters, especially the San Jacinto terns. In addition to these there are other seismic boundaries. branch and, to a lesser degree, the southern and northern parts For example, at the boundary between the Transverse Ranges of the Elsinore fault. The Newport-Inglewood fault zone is a and the Peninsular Ranges—especially where the Newport-In- well-marked trend even though no clearly visible, continuous, glewood and the San Jacinto faults approach the transverse historic, or even Quaternary fault rupture is present at the sur- Santa Monica and Cucamonga faults—there appears to be a face. The 1952 Arvin-Tehachapi earthquake and its numerous concentration of seismic activity. Another example is the appar- aftershocks are clearly related to the White Wolf fault when ent boundary between the area of extensive seismicity in the consideration is made for the dip of the fault. There is also a very- Coast Ranges province and the area of extremely low seismi- conspicuous north-trending concentration of epicenters along city in the Great Valley province. the 118° meridian from Nevada extending south into the Owens In a similar fashion, several of the sub-block structural bound- Valley of California, marking the historic ruptures on the Pleas- aries described earlier, are well marked by seismic activity. Espe- ant Valley (1915), Dixie Valley (1954), Rainbow Mountain cially good examples are the sub-blocks marked by the San (1954), Fairview Peak (1954), Cedar Mountain (1932), Excel- Jacinto, Elsinore, Palos Verdes, Calaveras, and Hayward faults. sior Mountain (1954), the Owens Valley (1872) faults (Table The coincidence of so many of these seismic boundaries and 4, Parts A and B). This particular seismic zone has been noted trends, with the structural provinces circumscribed by fault "118° in previous studies: it was called the Meridian Seismic trends, suggests a strong relationship. This relationship supports Zone" by Slemmons and others (1965) and the "Nevada Seismic the idea of the crust being divided into structural blocks and Zone" by Gump>er and Scholz (1971). sub-blocks which interact along their boundaries giving rise to The epicenter map shows what appear to be several aseismic the major earthquakes. The vast number of small, apparently areas within the state ( Plate 2C and 2D ). In the eastern Mojave random earthquakes in the state may be explained as events Desert area, from the Ludlow fault eastward to the Colorado occurring within these structural blocks and sub-blocks as a River, there is a total absense of earthquakes of magnitude 4 or response to minor crustal adjustments within the blocks them- greater; in this area, also, almost no faults having evidence of selves. Quaternary movement have been recognized. It may, however, be too early to conclude that this is truly an aseismic area be- CAUTIONS IN USE OF FAULT MAP OF cause: (1) our historic record is very short in years; (2) owing PLANNING to its extremely sparse settlement, the area has until very recently CALIFORNIA FOR LAND-USE been far from seismic networks capable of recording smaller earthquakes; (3) the short observational period may not reflect The Fault Map of California is a useful tool for considering the long-term seismic history, and the faults in the area may fault hazards in various parts of the state. However, it cannot be in fact be temporarily dormant; (4) most of the geologic map- overstressed that the nature and scale of the map pose severe pmg has only been reconnaissance and was not performed with limitations. First of all, more faults exist than are portrayed—the any special attempt to evaluate recency of faulting. (On the other limitations of the map scale alone (in which .32 cm [one-eighth hand, one would expect that any truly significant, extensive inch] on the map represents about 2.4 km [1.5 miles] on the Quaternary faulting would have been recognized, especially in ground) restricts what can be shown at 1:750,(X)0 scale. Second- this desert terrane where faults are so well-exposed and geo- ly, some faults are hidden beneath alluvium and other surficial morphic features endure for a long period of time.) deposits, or concealed by water; or they simply have not been Another apparent seismically quiet area encompasses the recognized because of insufficient geologic investigations. Also,

greater part of the Sierra Nevada, except for the southernmost it is important to remember that the map is a product of numer- part at the Tehachapi Mountians, and to a much lesser degree, ous sources, some of which are more detailed than others, and the northernmost part in theOrovillearea(Plates2Cand2D).Only that some observations were made by geologists whose objectives a very few magnitude 4 to 4.9 events occur in the larger central and purposes may not have included the evaluation of faults. part of the Sierra Nevada block. To the south, the White Wolf- Therefore, the degree of validity for the faults shown on the Walker Pass seismic lineament (and perhaps the Kern Canyon Fault Map varies from area to area. This is not only true for the 1985 TEXT TO ACCOMPANY THE FAULT AND GEOLOGIC MAPS OF CALIFORNIA 43

existence or extent of some faults, but sometimes in regard to age Borcherdt, R.D., editor. Studies for seismic zonation of the designations of fault displacement as well. Thirdly, not all the San Francisco Bay region: U.S. Geological Survey Profes-

faults shown in black should be assumed to be of pre-Quatemary sional Paper 941 -A, 102 p. age. Unfortunately this assumption has been made by some, even though the explanation on the map states that faults shown in Cluff, L.S., Slemmons, D.B., and Waggoner, E.B., 1970, black may also signify a "fault without recognized Quaternary Active fault zone hazards and related problems of siting displacement." The map explanation also has this to say about works of man: Proceedings, Fourth Symposium on Earth- faults shown in black: quake Engineering, University of Roorkee, India, p. 401- 410. Faults shown in this category should not necessarily be considered "dead." Evidence for recency of movement Grading Codes Advisory Board and Building Code Com- may not have been observed, or it may be lacking because mittee, 1973, Geology and earthquake hazards, planner's the fault may not be in contact with Quaternary deposits. guide to the Seismic Safety Element: Association of Engi- In many cases, the evidence may have been destroyed by neering Geologists (Southern California Section), 44 erosion, covered by vegetation, or by works of man. p.

Above all, the State Fault Map should not be used to replace Hart, E.W., 1980, Fault hazard zones in California: Califor- detailed site investigations for specific undertakings. For engi- nia Division of Mines and Geology Special Publication 42 neering purposes, faults at specific sites should be individually (Revised), 25 p. examined by detailed surface examination. Trenching, drill holes, and geophysical techniques may be helpful. Lung, R., and Proctor, R., editors, 1966, Engineering geol- Certain precautions must be specifically mentioned concern- ogy in southern California: Association of Engineering ing the offshore areas. offshore faults have The submarine shown Geologists (Los Angeles Section), 389 p. not been directly observed but rather interpreted from various remote-controlled devices. In addition, because of the difficulties Nichols, D.R., and Buchanan-Banks, J.M., 1974, Seismic in ship positioning, offshore faults may not be as precisely locat- hazards and land-use planning: U.S. Geological Survey ed as those on land. Factors such as the type of geophysical Circular 690, 33 p. equipment used, the depth to the sea floor, and the character of

the rocks and sediments below the sea floor afTect the quality of Sherard, J.L., Cluff, L.S., and Allen, C.R., 1974, Potentially the records obtained. active faults in dam foundations: Geotechnique 24, no. 3, This map should therefore be used only as an initial guide, or p. 367-428. as a first approximation, or for regional fault considerations. Before site-specific decisions are made, more information and Slemmons, D.B., 1977, State-of-the-art for assessing earth- maps on a larger scale should be consulted. The Fault Map of quake hazards in the United States, Report 6, Faults and California, by virtue of the area covered—an entire state, and a earthquake magnitudes: U.S. Army Engineer Waterways very large geologically very and complex one at that—must be Experiment Station Miscellaneous Paper S-77-8, 129 p., supplemented with additional data. Hopefully this this map and and Appendix, 37 p. Bulletin (especially the Index to the Source Data, Appendix D) will be useful as an introduction to the pertinent geologic litera- Ziony, J. I., Wentworth, CM., Buchanan-Banks, J.M., and ture and information on faults that were known at the time of Wagner, H.C., 1974, Preliminary map showing recency the compilation. These references should be considered an inte- of faulting in coastal southern California; U.S. Geologi - gral part in the understanding and use of the Fault Map of cal Survey Map MF-585, with 8 p. text. CaUfomia, for by referring to the documentation the reader can evaluate the interpretation given, and may possibly come to a different conclusion, especially if subsequent data have been gen- erated. DEPICTION OF VOLCANOES This Fault Map of California should not be confused with the "Special Studies Zones Maps" developed as a result of the Al- Distribution And Age quist-Priolo Special Studies Zones Act of 1972 amended (Hart 1980). The Special Studies Zones Maps, at a scale of 1:24,000, In addition to the faults, some 565 volcanoes are shown on the were conceived at a different time and for a different purpose, Fault Map of California. These consist mostly of cinder cones, and may not always agree in detail with the Fault Map of Cali- although volcanic domes and plugs, broad shield volcanoes, and fornia. The Fault Map of California, together with the Geologic a few strato-volcanoes (composite cones) are included. These Map of California were developed over nearly a nine-year period volcanic centers are associated with the vast outpourings of rela- largely preceding the Special Studies Zones Maps. It should be tively young lava and pyroclastic rocks depicted on the Geologic

clearly understood that no desire or intent is implied in the Fault Map of California (1977). The volcanoes shown are almost Map of California to either zone active faults or to predict where entirely of Quaternary age. Although volcanism has been very earthquakes, with or without ground rupture, might occur. active throughout most of California's geologic history, no at- No attempt is made in this volume to describe the methods tempt has been made to locate the older volcanoes because they geologists use in evaluating fault and/or earthquake hazards. were mostly ephemeral structures destroyed during the course of Publications on the subject abound and their numbers continue geologic time by erosion. to increase. The following partial list is submitted as an introduc- Of the volcanoes shown on the map, five were the centers of

tory guide: eruption in recent years (Table 6) . Many other volcanic centers are probably of Holocene age (less than about 11,000 years). Bonilla, M.G., 1970, Surface faulting and related effects, in These centers are located in such areas as Medicine Lake High- R.L. Wiegel, editor. Earthquake engineering: Prentice- lands-Lava Beds National Monument (Siskiyou and Modoc

Hall. N.J.. p. 47-74. counties), Inyo-Mono Craters (Mono County), Clear Lake area 44 DIVISION OF MINES AND GEOLOGY BULL. 201

(Lake County), and Amboy-Pisgah Craters (San Bernardino p. 1065). In fact, Mayo described the fault boundary between the County). Most of the volcanoes shown on the map are older than Sierra Nevada and the bedded sediments to the east as a deeply Holocene but less than two million years old. A few volcanoes penetrating zone of weakness that opened many channels for the

shown on Geologic Data Map No. 1 are of Pliocene age (two to extrusion of lava and the location of volcanoes (Mayo, 1941, p. five million years old). 1064-1069).

According to Koenigand others (1972, p. 1,4), the extrusions Table 6. Observed volcanic events in California (modified in the Coso geothermal area, Inyo County, consisting of a mix-

after C.W. Chesterman, 1971). ture of explosion breccia rings, perlite domes, and obsidian sills, are fracture-controlled. Inspection of the geologic map of the 1951 Violent eruption of mud-volcanoes and hot water dis- Haiwee Reservoir quadrangle (Stinson, 1977) shows conspicu- charge at Lake City. Modoc County. ous north and northwest alignments of volcanic centers. These may be fault controlled, perhaps by a buried north-trending fault 1914-17 Eruption of Mt. Lassen, lava flows, ash falls, flows, mud zone and a northwest-trending fault zone. More recent geologic, and nu6es ardentes. geophysical, and geochemical studies in the Coso area suggest that the youngest volcanic rocks, the rhyolitic dome field, and 1890 Eruptions in Mono Lake, including emission of steam, the associated fumaroles lie at the center of a ring-fault structure sulfurous fumes, boiling water, and hot mud. superimposed on regional fault patterns and overlying a young 1857 Ash eruption from either Mt. Lassen or Mt. Shasta. magma chamber (Duffield, 1975; and ERDA 77-74, p. 65). Allen and others (1965, p. 761) have shown that Cerro Prieto, 1851-62 Eruption of Cinder Cone and associated lava flows. a Quaternary cone, 35 km south of the Mexican border, lies east of Lassen Peak. squarely athwart the extended trace of the Quaternary San Ja- cinto fault. 1786 Eruption of steam and ash from either Mt. Lassen or In San Luis Obispo County, 14 intrusive volcanic plugs are Mt. Shasta (observation of La Perouse while sailing aligned over a distance of approximately 32 miles) along the California coast). km (20 (see Figure 13) through the town of San Luis Obispo to Morro Rock (and offshore, according to H.C. Wagner, 1974). These Tertiary plugs, although much older than the Quaternary volcanoes shown on the Fault Map of California, appear to be another Relation of Volcanoes to Faults example of emplacement of volcanic centers along a zone of

weakness that in all probability is a fault even though a fault The relation of volcanic centers in California to faults remains trace has not been observed in the field. a subject of controversy, although there are certainly several

places in the state where there is clear evidence or strong sugges- EXPLANATION tion of such a relationship. For example, Howel Williams (1934, [H Ouolcrnarir p. 232) pointed out that the alignment of five plug domes, two dcpoiiti cinder cones, and one lava cone suggests a through-going frac- m T«rl.O(y ture passing across the summit of Mount Shasta even though no maiinc rockt surface displacements are to be seen along this trend. Similar Crdoctoui alignments can be seen on the maps by Gordon Macdonald in maont lockk the Lassen Peak area. The close alignment of nine cinder cones FroncitCOn east of Crater Peak (Manzanita Lake quadrangle), about 19 km CompUi

(12 miles) north of Lassen Peak, is strongly suggestive of fault Cr«tae«ou» gianilic or fissure control, as is the alignment of at least 19 cinder cones rochi in the eastern part of Lassen National Park, south-easterly from Poison Lake, on the Harvey Mountain and Prospect Peak quad- Tvilisri rangles (Macdonald, 1963, 1964, 1965). •Cconic plug

The arcuate alignment of more than 1 5 volcanic eruptive cen- » T«ri>o>y volconic ters south of Mono Lake, including the rhyolite domes of Mono plug Itubntorint) Craters, is a classic example of fault-controlled volcanoes (Fig- ure 6). Russell (1889) was probably the first to conclude that the Mono Craters were probably localized along faults (related Figure 13. Alignment of Tertiary volcanic plugs near San Luis Obispo along to the faults along the east scarp of the Sierra Nevada). Mayo o line of weakness presumed to be an ancient fault. and others (1936) described the structures in the rhyolite domes south of the Mono Craters and concluded that they are deter- Volcanic Hazards mined by faults in turn controlled by northwest-striking joint sets in the bedrock. Kistler (1966) proposed that the arcuate Volcanic eruptions have commonly occurred throughout Cali- traces of faults are not related to joint sets but to a zone of fornia's long geologic history, and numerous eruptions have oc- weakness thought to be related to the early cooling history along curred in relatively recent geologic time, as indicated by the large the border of a quartz monzonitc pluton. In any event, the number of volcanoes depicted on the Fault Map of California. existence of a fault control beneath the line of Mono Craters was, Volcanism has occurred in California approximately 65 years ago

in fact, confirmed dunng the construction of the Los Angeles with the violent eruption of Lassen. It would therefore seem Water District tunnel (Putnam. 1949, p. 1299). reasonable to expect other eruptions in the state, although exact-

Another clear example of fault-controlled volcanoes is the ly when or where is uncertain. The most probable centers of Quaternary (possibly 1872) fault scarp that trends between the future volcanic eruptions are in areas where past eruptions have volcanic cones of Red Mountain and Crater Mountain, in Owens occurred and particularly at large central-vent volcanoes (Mil- Valley south of Big Pine (Allen. 1965. p. 761; and Mayo. 1941. hneaux. 1976). .

1985 TEXT TO ACCOMPANY THE FAULT AND GEOLOGIC MAPS OF CALIFORNIA 45

The Urban Geology Master Plan for California (Alfors and Mode of Occurrence Of Hot Springs others, 1973) estimates that losses due to future volcanic erup- tions could amount to $50 million between 1970 and the year Thermal springs in California are probably associated with or 2000. The report concludes that major urban areas of the state controlled by one or more of the following geologic conditions: are relatively safe from the threat of volcanic eruptions.

(1) areas of volcanoes of geologically recent activity

DEPICTION OF THERMAL SPRINGS (2) frictionally heated rocks associated with faults

AND WELLS (3) intensely deformed mountains

Besides faults and volcanoes, 584 thermal springs and wells (4) jointed or faulted batholithic rocks are also plotted on the Fault Map of California. Separately iden- tified are the locations of high temperature mud volcanoes and 1 In some areas of volcanic rocks, especially in areas of recent- mud pots at Wister (Imperial County), Lake City (Modoc ly active volcanism, magma or solidified magma, probably lies County), and the unusually prolific carbon dioxide springs and below the surface that has not cooled to normal temperatures, wells at Niland (Imperial County) and Hopland (Mendocino and water coming near it will be heated. In a few places—at The County). Many of the hot springs are clearly associated with Geysers area of Sonoma County, for example— it is believed that known faults or volcanic rocks. a hot spring is not Where shown heat from magma at depth has been transmitted to the overlying associated with a fault, it may indicate that the area has not been rock. Meteoric water penetrating near the hot materials is thus mapped in sufficient detail. heated. Faults and fractures may serve as conduits bringing the The location of hot springs and wells serves as an approximate hot water to the surface. guide to areas of anomalously high temperatures present today in the crustal rocks of California. This, of course, is pertinent in 2. Rocks along fault zones are heated considerably by the great the exploration of geothermal power sources. In volcanic areas, pressure and friction that are produced by extensive masses of the location of hot springs may indicate either a dying phase of rock moving past one another. This is evidenced by the presence volcanism or a precursor of volcanic activity. of fused mylonite or crushed rock along certain fault zones Information concerning temperatures, more specific location (Wallace, 1976). In an analysis of faulting, McKenzie and data, well depths, date drilled, and pertinent references is con- Brune (1972) have shown that a temperature of 1000°C can be tained in Appendix B. obtained by frictional heating along a fault, with actual melting taking place along the fault plane. When water comes in contact with a fault zone, fault gouge can act as a barrier to lateral Temperature migration, and the crushed zone adjacent to the fault gouge can serve as a conduit for water to reach the surface. Thus, if water passes upward near recently active faults, the water can take up Following the convention established by G.A. Waring's re- heat by contact with the frictionally heated rocks. jxjrts (1915 and 1965), which were the principal sources used when this present compilation was started, the writer considered 3. It can be reasonably assumed that accompanying intense as thermal only those springs that are more than 15°F (8.3°C) deformation of crustal rocks by folding and faulting, a considera- above the mean annual temperature of the air at their localities. ble amount of thermal energy is generated. Furthermore, a sig- In the case of drilled wells, a normal thermal gradient of about nificant portion of the thermal energy is expected to remain VF increase for each 100 feet of depth (2°C for each 100 meters) stored over a certain interval of geologic time (Chaterji and was taken into consideration when determining whether the well Guha, 1968). For example, only comparatively recent (Tertiary should be classified as thermal. or post-Tertiary) deformation might be expected to account for The water from thermal springs may be meteoric—that is, the heat-flow of certain thermal springs. A good example of this surface water that has percolated downward, been heated, and may be a comparison of the abundant warm springs in the Late then ascended to the surface. Or, thermal water may be juvenile Tertiary-Quaternary highly deformed Coast Ranges with the —that is, a product from the magma; water which has reached almost total absence of thermal springs in the Klamath Moun- the surface for the first time. Thermal spring waters also may be tains—the intense deformation of the Klamaths having largely a mixture of meteoric and juvenile water. Methods of distin- taken place in pre-Tertiary time. guishing between juvenile and meteoric waters by major and minor element chemistry, isotope ratios, and other means are 4. Deep joints or faults in batholithic rocks, like those in the described by White (1969). Sierra Nevada, occasionally give rise to moderately warm The abnormally high temperature of hot springs and wells springs. Meteoric waters collected in such cracks may be heated may fluctuate or even normalize, and some springs and wells by the disintegration of radioactive elements in the granitic rocks may "dry up" or cease to flow. One of the factors commonly (Kiersch, 1964, p. 43). accounting for these phenomena in California is the occurrence of earthquakes. Another factor commonly affecting springs is the precipitation of calcium carbonate, which causes clogging, resulting in reduction of flow and ultimately cessation. Distribution Of Hot Springs Springs close to boiling-point temperatures are found in many localities in the state. Because the boiling point decreases with Hot springs in California have a wide geographic distribution. an increase in elevation, the boiling temperature of springs in Because the state is readily divisible into 1 1 geomorphic prov- California ranges from 212°F (100°C) at sea level to about 185°F inces, each reflecting fundamental differences in geology (Figure (85°C) at 14,250 feet (4377 m). Table 7 summanzes the loca- 14), Cahfomia's thermal springs will be discussed in relation to tions of springs near the boiling point in California. these provinces. Although no consistent or clear relation of the 46 DIVISION OF MINES AND GEOLOGY BULL. 201

Table 7. Springs near boiling point temperature.

STAU MAP

SHEET . 1985 TEXT TO ACCOMPANY THE FAULT AND GEOLOGIC MAPS OF CALIFORNIA 47

hot springs to the four previously mentioned geologic modes of is highly faulted, and the source of heat is probably a magma occurrence discussed is always discemable, where these condi- chamber at shallow depth (Chapman, 1957). tions are recognized, they will be briefly described. Moderately warm springs are scattered in the central and

The Modoc Plateau in northeastern California is a region of southern parts of the Coast Ranges province in highly folded and extensive Late Tertiary and Quaternary lava flows and vol- faulted Mesozoic and Tertiary strata. Likewise, the Transverse canoes. Within these volcanic rocks are hot springs that probably Ranges is a highly folded and faulted province marked by a derive heat from the same source as the lava outpourings. Al- number of thermal springs, including the near-boiling Sespe Hot though the area is largely mapped only in a reconnaissance way, Springs in the Santa Ynez Mountains. The Sesi>e Hot Springs are often the thermal springs appear to be fault controlled. situated within the Pine Mountain fault zone. In the eastern part

Immediately east of the Modoc Plateau is Surprise Valley in of the Transverse Ranges, in the San Bernardino Mountains, are the Basin Ranges province, a province characterized by vol- the Arrowhead Springs. This group of boiling springs is also on canism and block faulting. Here, five boiling springs and four a fault, probably a splay of the San Andreas fault. thermal wells are aligned along the Surprise Valley fault, a major The Peninsular Ranges province, in the southwestern part of Quaternary fault with vertical movement estimated in excess of the state, has a number of warm springs. These springs he close 1650 m (5500 feet) (Gay, 1959) and associated with promi- to the Elsinore and San Jacinto fault zones. The thermal springs nent gravity and magnetic anomalies. It also has evidence of Late in the Peninsular Ranges province, the central and southern Quaternary activity. Several other springs in California's Basin Coast Ranges, and the Transverse Ranges are all outside areas Ranges province, some at boiling temperature, occur in the of geologically recent volcanism (although containing volcanic Honey Lake volcanic area. The springs are situated along the rocks of earlier geologic time). These provinces, however, are Quaternary Amedee and Litchfield faults and, farther to the among the most active tectonically, and are traversed by numer- south, in the Coso Mountains, on faults in an area of Quatenary ous major faults. These provinces are also intensely folded and, volcanism. in places, as for example the western Transverse Ranges, are still Two of California's most famous volcanoes. Mount Shasta undergoing active deformation by folding, uplift, and faulting. and Lassen Peak, lie in the southernmost end of the Cascade The Salton Trough is essentially a graben or down-faulted Range province. This province consists of a chain of volcanoes block. Numerous mud volcanoes and hot springs are situated extending into Oregon and Washington. Mount Shasta and Las- principally along or near the active San Andreas fault zone on sen Peak, both active in historic time, are the sites of several hot the east side of the graben. For example, shallow hot water wells springs, steam vents, and fumaroles. The associated hot springs occur at Desert Hot Springs, a hot spring is found at Dos Pal- are clearly related to recent volcanism and probably to faults. mas, and numerous mud volcanoes occur at the southeastern end

The Sierra Nevada province is bounded by a profound fault of the Salton Sea. Also in this fault trough, numerous explora- on the east side, which is the loci of several hot springs, especially tory wells have tapped high temperature steam and brine on where geologically recent volcanism has occurred, such as at the some of the largest known geothermal anomalies of the state. Mono Lake, Casa Diablo, and Owens Lake areas. The south- One of these geothermal anomalies, at Niland, is associated with central part of the Sierra Nevada batholith is also the site of relatively young volcanic rocks which are dated at 16,000 years several warm springs. Here hot water issues from granitic and (Muffler and White, 1969). Positive gravity and magnetic anom- metamorphic rocks far removed from young, volcanic rocks. alies suggest the presence of intrusive bodies at shallow depth. The springs appear to be related to the Kem Canyon fault along The Mojave Desert province, although containing both exten- which they lie. As suggested earlier, the heat may be derived sive volcanic rocks of recent geologic age and numerous exten- from the disintegration of radioactive elements in the granitic sive Quaternary faults, is nearly devoid of thermal springs. This rock. The Kem Canyon fault, although a major tectonic feature, is probably attributable to the dearth of water rather than to the is probably not active, inasmuch as undisturbed Pliocene vol- lack of a subterranean heat source. canic rocks are known to lie athwart the trace of the fault. The Klamath Mountains province in northwestern California, Hot springs in the northern part of the Coast Ranges province with abundant water, and lying in an intensely deformed terrain, in California are both numerous and among the hottest in the has only one known abnormally high temperature spring. This state. Most of them are associated with the Clear Lake and may be due to the lack of geologically recent volcanism or to the Sonoma volcanic areas, or lie in the intensely faulted and de- great geologic antiquity of the deformation, in which case any formed Mayacmas Mountains. The Clear Lake Volcanics are thermal energy generated from these movements would proba- late Pliocene to Holocene in age (Heam and others, 1975) and bly have dissipated during the long period of conduction and the older Sonoma Volcanics are Pliocene. The Mayacmas Moun- radiation. Another possibility might be related to the huge abun- tains lie between the Clear Lake and Sonoma volcanic areas. dance of ground water (one of the highest rainfall areas of the Here, in the world-famous area of The Geysers, is the first (and state) that is available to mix with and cool to normal tempera- at present, the only) commercially developed geothermal power tures any hot water that rises from the underlying rocks. source in the United States. The Geysers are situated in meta- The remaining natural province of the state, known as the morphosed, sedimentary, and volcanic Mesozoic rocks of the Great Valley, is essentially a gigantic alluvial plain containing a Franciscan Complex, and although no geologically recent vol- tremendous thickness of sediments. It is not surprising that no canic rocks are exposed, the area is marked by numerous fuma- thermal springs (or thermal wells) occur in this province, for it roles, steam vents, and other signs of active volcanism. The area lacks a known subterranean heat source. 48 DIVISION OF MINES AND GEOLOGY BULL. 201

iO 1. BASIN RANGES 2. MODOC PLATEAU 3. CASCADE RANGE 4. KLAMATH MOUNTAINS 5. COAST RANGES ®\ : 6. GREAT VALLEY 7. SIERRA NEVADA •••• • 8. TRANSVERSE RANGES

9. MOJAVE DESERT 10. PENINSULAR RANGES 11. SALTON TROUGH

*a \K ©N®\ ®

.....*^ \ V © V ©

8^ ^8

..•••. *. ^

.:r ®

Figur« 14 Relief Map of Californio ihowing geomorphic provinces. PART II GEOLOGIC MAP OF CALIFORNIA

The Man with the Hammer

A wanderer—with downcast eyes he looks For truth 'mid ruins and the dust of Time. The strata of the mountains are his books Wherein he reads, as he does slowly climb.

—-A.C. Lawson University of California Chronicle October 1925

GEOLOGIC MAP OF CALIFORNIA

INTRODUCTION fornia State Mining Bureau. Beginning with this map, the re- sponsibility for preparing and publishing succeeding editions of relatively large-scale geologic maps of California has remained More than 90 years have passed since the preparation in 1891 with the State. Only eight geologic units were depicted on the of the 1:750,000 scale Preliminary Mineralogical and Geological 1891 map; however, their general relations are better shown than Map of the State of California. The 1977 edition of the Geologi- on all the previous geologic maps. Special emphasis was given to cal Map of California is the latest in the series of statewide mineral resources. Such units as auriferous gravel, auriferous geologic maps published by the State, and represents a great step slate, and limestone are portrayed, and the locations of known forward in the mapping and understanding of California's geol- mineral deposits are shown. The map was issued by the State ogy. (See Table 8 for list of State geologic maps of California.). Mineralogist, William Ireland, but the map compiler is not cred- ited on the map. However, the 10th Annual Report of the State

Mineralogist (Ireland, 1890, p. 21) states that the topographical and other work on the Preliminary Geological and Mineralogi- HISTORY OF cal Map was "being executed by Mr. Julius Henkenius, who received aid in the geological and mineralogical locatings from GEOLOGIC MAPS OF CALIFORNIA the Field Assistants."

Geological Map of the The First Attempts State of California— 1916 Geologic mapping in California began about 160 years ago. The first geologic mapping in the state, done by Lieutenant Twenty-five years after the 1891 Preliminary Mineralogical Edward Belcher, a British naval officer, was a remarkably accu- and Geological Map of the State of California, another 1:750,000 rate geologic map of the Port of San Francisco. Although Belch- scale state geologic map was published by the California State er did the surveying for the map in 1826. it was not published Mining Bureau. This map was prepared by J. P. Smith, Professor until 1839. This map and other early geologic maps of California of Paleontology at Stanford University, and was accompanied by are described and illustrated in "State Geologic Maps of Califor- a brief bulletin describing the geology (Smith, 1916). nia—a Brief History" (Jennings, 1966). The map legend lists 21 geologic units. Although Professor Landmarks in the publication of early geologic maps of the Smith's bulletin clearly explains that certain areas of California entire state begin with the hand-tinted geologic map of Califor- were still unmapped, his map, unlike the earlier 1891 edition, nia made by W.P. Blake in 1853 and published in Volume V of shows the entire area of the state covered by colors representing the War Department's "Report of Explorations in California for geologic units with delineated contacts. This, unfortunately,

Railroad Routes" (Blake, 1857). Utilizing nine geologic units, leaves the map-user without any clue as to what is known and this 41 X 56 cm (16 x 22 inch) map was the first published what has merely been projected. The absence of geologic faults geologic map that specifically and exclusively pertained to Cah- on this map is also somewhat puzzling. Although faults were by fomia. This map was followed by the first color-lithographed this time widely recognized and mapped—as, for example, in the map of the state, made in 1 867 and published four years later in atlas accompanying the "State Earthquake Investigation Com- Paris as part of a report of a French scientific mission to Mexico mission" report on the disasterous 1906 San Francisco earth- and the "ancient Mexican possessions of the north" (Guillemin- quake—not even the San Andreas fault is shown on the 1916 Tarayre, 1871). The geology is portrayed in a most impressive geologic map of California. manner by ten geologic units, and the geologic interpretation is By 1916, there was much outstanding geologic mapping to much improved over Blake's map. draw upon. U.S. Geological Survey geologists H.W. Turner, The second color-lithographed geologic map of California was Waldemar Lindgren, J.S. Diller, F.L. Ransome, G.H. Eldridge, prepared by another Frenchman, Jules Marcou (1883), and Ralph Arnold, Robert Anderson, R.W. Pack, and H.W. Fair- published in the "Bulletin of the Geological Society of France." banks had completed a number of geologic folios and bulletins The nine geologic units shown were largely based on Marcou's on the Sierra Nevada gold belt area, the Coast Ranges, and the observations while working with the Pacific Railroad Survey in oil regions of the state. In addition, many significant contribu- 1854 and the Wheeler Survey West of the 100th Meridian in tions had been made by Professor A.C. Lawson and graduate 1875, both Federal surveys. The map was accompanied by a students at the University of California and by Professor J.C. report on the geology of California. Branner and his students at Stanford University. These early, page-size geologic maps of the state were su- The 41-page bulletin, "The Geologic Formations of Califor- perseded in 1 89 1 by the first relatively large-sc£tle statewide geo- nia," which accompanies the 1916 Geological Map of California, logic map. consists of the following: an expanded legend for the reconnais- sance geologic map; a description of the geologic record of Cali- Preliminary Mineralogical and Geological fornia as related to the fluctuations of the "Great Basin Sea" and the Pacific Ocean; a description of the "rock-forming agencies Map of the State of California — 1891 of California" wherein the formation of igneous rocks, organic and inorganic sediments, and chemical deposits are briefly dis- The Prelimmary Mineralogical and Geological Map of the cussed; a listing of the sources of data for the geologic map; and, State of California, at a scale of 1:750,000 (12 miles equals one lastly, a listing of the formations included in each geologic unit inch), was prepared and published in four sections by the Cali- shown on the map.

51 52 DIVISION OF MINES AND GEOLOGY BULL. 201

Table 8. State geologic maps of California.

DATE OF MAP I<585 TEXT TO ACCOMPANY THE FAULT AND GEOLOGIC MAPS OF CALIFORNIA 53

Lake Tahoe using 300-foot contours, and for Salton Sea using Table 9. Geologic Atlas of California (I-.250,000 scale). 10-foot contours. before the retirement of Dr. Jenkins, Charles Shortly Jennings MAP SHEET was put in charge of the map compilation and Rudolph Strand (by order of and James Koenig were added as assistants. One of the greatest publication] problems facing the compilation project at the onset was deter- mining the existence of all the new source data. The U.S. Geolog- ical Survey's excellent index to published geologic maps of California (Boardman, l'^52) was several years out-of-date, and no map index to doctoral dissertations and master's theses spe- cifically on California geology existed at that time. Largely through the efforts of Rudolph Strand, an index to published geologic maps was prepared. This index updates the Boardman index through 1956. Approximately 256 entries were added, and the boundaries of all the entries were plotted on a new format using the Army Map Service one degree by two degree quadrangle units. The index proved to be so valuable in other areas of the Division's work and to geologists and others outside the Division that it was made available by publication (Strand and others, 1958). Similarly, an index to graduate theses on California geology was prepared in order to identify and tap the enormous wealth of geologic mapping available from this source. For many areas of the state, unpublished doctoral dissertations and master's theses were the only source of geologic information; hence these were essential to the preparation of the State Geologic Map. The first such index covered the span of time from 1892 (the earliest recorded thesis on a California area) through 1961, and also was published by the Division (Jennings and Strand, 1963). From time to time various staff members were assigned to the "State Map Project." These geologists worked either on a full- time basis to compile one or more sheets (Table 9), or part-time principally for field mapping to fill in "blank areas" or to prepare additional source data indexes (see "Indexes to published geo- logic maps" and "Indexes to theses" listed under "Other Refer- ences" in Appendix D). Compiling the Geologic Atlas turned out to be more difficult than anticipated. At the outset of the project, the difficulties associated with compiling a geologic map of the entire state, with all of its geologic diversity and complexity, were for the most part recognized, but it was hoped that the abundance of new data on hand would make overcoming these difficulties fairly simple. Actually, the inconsistent nature of these new data made the task more difficult. The source maps for some areas of the state were excellent; in other areas they were very poor, incomplete, or simply nonexistent. Frequently, well-described areas were adja- cent to poorly understood, incompletely mapped, or totally un- mapped areas. Often, too, there was no continuity between maps for adjacent areas because of differences in geologic interpreta- tion. Thus, the compilation could easily have resulted in a patch- work of data. Fortunately, perhaps, the scale of the atlas made it possible to ignore a multitude of discrepancies. Numerous problems, however, had to be resolved in the field, and almost all blank areas in the state were filled in by a series of reconnais- sance mapping programs undertaken by various Division per- sonnel. Nevertheless, in a few areas of complex geology, or where particularly detailed work was surrounded by less detailed map- ping, white areas were left around the more detailed area to preserve as much information as possible. Blank areas marked on the atlas sheets as "unmapped" or "incomplete" actually amount to a very small percentage of some map sheets and are absent entirely from others. To provide geologic data for the large areas of the state for which there were no published or unpublished maps or theses available, the Divi- sion's reconnaissance geologic mapping program was initiated in 1957. The first mapping by the Division for this purpose was 54 DIVISION OF MINES AND GEOLOGY BULL. 201

Perhaps the most widespread and inaccessible area mapped by Two Small-Scale Geologic Mops of the Division lay in the high Sierra, extending from near Lake Tahoe at the north to the Tehachapi Mountains at the south. California (1966 and 1968) This mapping provided data for about half of the Fresno Sheet and parts of the Walker Lake, Mariposa, and Bakersfield Sheets. Two relatively recent lithographed maps of the state, although The main objective of this reconnaissance work was to block out of much smaller scale than the previously described maps, the major roof pendants in the Sierran batholith that heretofore should be mentioned. The first of these was compiled jointly by had not been mapped, and to delineate the remnants of volcanic the U.S. Geological Survey and the Cahfomia Division of Mines deposits and extensive glacial deposits. Much of this area was and Geology at a scale of l;2,50O,(X)O. It was published by the only accessible by backpack or horse and, because of the high U.S. Geological Survey (1966) as "Miscellaneous Geological 1-512" elevation and snow, could only be mapped during the summer. Investigations Map and has been reprinted or copied in Fourteen Division geologists contributed to this concerted effort several different formats in various other publications. This before the job was completed, with the major part done by J.L. highly diagrammatic map vividly portrays the major rock units Burnett, R.A. Matthews, and C.W. Jennings. by 1 1 subdivisions—three Cenozoic (marine, nonmarine, vol- canic), three Mesozoic (principally sedimentary), one Paleozoic The final sheet was completed in 1968 and published in 1969. (sedimentary and volcanic), one Precambrian (all rock types), Collectively, these works make up the Geologic Atlas of Califor- a Pre-Cenozoic metamorphic rock unit, Mesozoic granitic rocks, nia, which consists of 27 sheets, 1 10 pages of explanatory data, and lastly, ultramafic rocks. Faults are shown with heavy black a master legend, and a formation index. lines, and direction of apparent movement is indicated by ar- The geologic legend for this atlas consists of 124 cartographic rows. The base is without roads, and only a few major cities and units. In a state as geologically complex as California, with geographic features are identified. This map effectively displays formations representing every geologic period known in the the most prominent geologic features of the state, and has en- world, the choice of units to show statewide such variety and joyed considerable popularity. diversity in a meaningful way required some special innovation. The second map was prepared and published by the American Olaf P. Jenkins worked out an admirable legend for the 1938 Association of Petroleum Geologists (1968) as part of their map, and this with only a few modifications, was also used for Geologic Highway Map Series. It includes Nevada as well as the atlas series. At first glance, the legend appears to be based California and is at a scale of 1 inch equals approximately 30 principally on age, with the exception of two formations, the miles. Twenty-nine geologic units are depicted, but because their Franciscan and Knoxville (which are very widespread in the identification is obscure and their description is scattered among California Coast Ranges). In actuality, the geologic contacts five separate legends, five columnar sections, and lengthy explan- shown are drawn on the basis of rock-stratigraphic units (forma- atory notes, using the map is cumbersome. The back of the map tions) and not time-stratigraphic units. The procedure followed is filled with cross sections, a geologic history, a physiological was to group the numerous formations into "State Map Units" map, and a tectonic map. according to (a) their relative stratigraphic position (usually expressed by age); (b) their fundamental rock type (sedimen- tary, metasedimentary, igneous, and meta-igneous); (c) their environment of sedimentation (marine or non-marine); and (d) GEOLOGIC MAP OF CALIFORNIA— their broad modal composition (in dividing volcanic and pluton- ic rocks such as rhyolite, andesite, and basalt, or granite, 1977 granodiorite, and tonalite) . Genesis was the basis for subdividing the various Quaternary units (for example, dune sand, salt History of the Project deposits, lake deposits, glacial deposits, and terrace deposits, with the alluvium of the Great Valley province subdivided into Even before the 1:250,000 scale Geologic Atlas of California stream channel deposits, fan deposits, and basin deposits—inter- was completed, it was recognized that a smaller-scale map of the preted largely from federal and state soil survey maps). state, one that would present an overview of the geology of the prominent or well-known faults are identified by The more entire state, was highly desirable. It had become apparent that to distinguish faults name; however, no attempt was made by age the individual atlas sheets, as useful as they were for field and of latest movement. office purposes, were not satisfactory for evaluation of statewide sheet is Accompanying each map an explanatory data sheet geologic and structural trends. Therefore, late in 1965, plans that includes an index to the geologic mapping used in the com- were made for a 1:750,000 scale map of California (Jennings, pilation, a table of stratigraphic nomenclature for the units com- 1965). piled on that sheet, and an index map indicating the U.S. After consideration of various scales, 1:750,000 was chosen Geological Survey topographic quadrangles within the map because the resulting size, about 1.4 x 1.5 meters (4.5 x 5 feet) sheet area. Aerial oblique photographs of salient geologic fea- is convenient for fitting on an average office or classroom wall. tures in the sheet area illustrate most data sheets. map In addition, this scale is consistent with the first two official The map is not specifically designed as a wall map of Califor- geologic maps of Cahfornia published by the State in 1891 and nia, but rather as an atlas, suitable for use in the field as well as 1916, and the scale is also sufficiently large to show a significant in the office. Should the entire map be assembled, however, (as amount of geologic information. has been done in several universities and in the former Division Almt)st two years passed, however, before work on compiling Headquaters office in San Francisco), it covers an area about 4.6 this new map could begin. A pilot compilation of the Chico Sheet X 4.3 meters (15 x 14 feet). Although the sheets were published area, using a newly devised legend, incorporating such new data individually over a period of 1 1 years, all the colors and patterns necessary for classifying the faults, and adding fold axes and of the geologic units were integrated as closely as possible so that other structural data, was then started by C.W. Jennings. It soon adjacent sheets match in continuity of units and color. Thus, became apparent that considerable updating of the geologic data adjacent sheets can be trimmed and joined in any size block, if for most of the map sheets would be necessary because many of desired. the published atlas sheets were already several years old and a 1985 TEXT TO ACCOMPANY THE FAULT AND GEOLOGIC MAPS OF CALIFORNIA 55

large quantity of new geologic map data was available for a good ent. This is not the case, however, with a geologic map of the part of the state. state, the use of which is difficult to explain to the nongeologist. At the beginning of the project, it was decided that a multipur- Dr. P.B. King and H.M. Beikman of the U.S. Geological Survey f)Ose map of the state would be most desirable. In addition to the discussed this difficulty in their explanatory text for the Geologic geology, the map would emphasize recently active faults, recent Map of the United States (King and Beikman, 1974). Their

volcanic rocks and volcanoes, thermal springs, offshore struc- explanation is succinctly expressed, and because it applies as well

tures, and major fold axes. Therefore, all these data were plotted to the Geologic Map of California as it does to the Geologic Map

on the work sheets; but it became evident that, for publication of the United States, we quote at length from it here:

purposes, it would be much more effective to separate some of Sometimes, when we explain to nongeologists our project this information and make two maps rather than one. Pursuing for a Geologic Map of the United States, we are dismayed this concept, it was planned to present a series of maps at the when asked, "What good is it?" We compilers, enmeshed same 1:750,000 scale illustrating various geologic and geophysi- in our many problems of assembling, collating, and gener- cal parameters that can conveniently be studied individually or alizing the source data for the map, find it difficult to in relation to one another. Thus, the first map in this series is the produce a ready answer to this question. Nevertheless, the Fault Map of California With Locations of Volcanoes, Thermal values and uses of an accurate geologic map are manifold, Springs and Thermal Wells. The Geologic Map of California is not only to geologists, but to the public at large. Geologic Data Map No. 2. The third in the series will be a

Gravity Map of California, which is nearing completion.* Other First of all, of course, the map displays the rocky founda-

maps in the series, such as an epicenter map and aeromagnetic tions on which our country is built and is a summation of map, are in the planning stage. In addition, consideration is the nearly two centuries of investigation of this foundation

being given to periodically update and revise the Fault Map of by a succession of geologists. It is thus a reference work California, because of the rapid rate at which new information that present and future geologists of the country can con- is being generated and because of the growing demand for such sult and is of prime importance in the education of earth

data in city and county seismic safety planning, and in the loca- scientists in schools and colleges. Further, it can be con- tion of schools, hospitals, nuclear power plants, and other engi- sulted by geologists in other countries and continents who neering works. wish to learn about the geology of the United States; they A preliminary draft of the 1:750,000 geologic map was com- will compare the map with similar national or continental plete in 197 1, and it accompanied a report entitled "Urban Geol- maps of their own countries. ogy Master Plan for California" (Bruer, 1971), which was In terms of resources useful to man, the Geologic Map lays financed by the Federal Department of Housing and Urban out accurately the major regions of bedrock in the United Development. Many areas on the map, however, were still shown States upon which many facets of our economy depend. It in a tentative state and the map needed additional work pending illustrates the areas of stratified rocks that are the sources receipt of new information. The map also required more editing of most of our fuels, and the areas of crystalline, plutonic, and generalization in complex areas. This work was accom- and volcanic rocks that contain important parts of our plished and the compilation was complete in 1972. mineral wealth. The map shows areas of complex folding Because of the complexity of the map, a hand-tinted copy of and faulting, parts of which are still tectonically unstable the map was carefully prepared and then photographed and and subject to earthquake hazards. To some extent the full-scale color prints were made. These colored prints proved bedrock represented on the map also influences the surface very helpful in the extensive reviewing process that the map then soils, which are of interest in agriculture and engineering underwent by more than forty-five geologists conversant with works. California geology. Reviewers from outside the Division includ-

ed personnel from the U.S. Geological Survey, universities, other Beyond this, the practical value of the map is less tangible,

federal and state agencies, and a number of consulting geologic although it can be an important tool for the discerning firms. The review was completed in about six months, and exten- user. Clearly, the map will not pinpoint the location of the sive revisions and additions were then made to the master compi- next producing oil well or the next bonanza mine, nor will

lation. Because of the demand for the information on this map, it give specific advice for the location of a dam or a reactor an uncolored version of the original hand-drafted compilation site; these needs can only be satisfied on maps on much was published (see "Preliminary fault and geologic map of Cali- larger scales, designed for specific purposes. Nevertheless,

fornia 1973" I — in Part of this report). Work also began in the sapient exploration geologist can find upon it signifi- scribing and preparing the plates for the fault map portion of the cant regional features not apparent to the untrained user. compilation. Scribing of the geologic contacts for the "Geologic Important mineral deposits cluster along regional tec- Map of California" did not begin until January 1975, when tonic trends or chains of plutons of specific ages. Final- drafting help became available. During the final stages of scrib- ly, the Geologic Map will be used in national planning ing and preparing of the printing plates, some additional correc- activities in conjunction with other national maps showing tions of the geology were made, and new data for a few selected environmental features such as climate, vegetation, and areas were added. The bulk of the data shown, however, is land use—for the location of power transmission corri- only complete to 1973. dors, highways. National Parks, wilderness areas, recla-

•Editor's nole: Geologic Data Map No. 3, Gravity Map of California and its mation projects, and the like. Continental Margin, and Geologic Data Map No 4. Geotherma! Resources Map of California, ha\c been published since this was writtcn. In essence, the Geologic Map of California is simply a repre- sentation of a part of the earth's surface. It shows the distribution of the rock units that occur at the surface, and tells us something Uses Of The Geologic Map of their composition and origin, as well as their relative degree of hardness—a clue to their resistance to erosion. In addition, the The usefulness of the Fault Map of California, whose intimate map shows by appropriate symbols where and how the rocks are relationship to earthquakes is easy to explain, is generally appar- folded and faulted. 56 DIVISION OF MINES AND GEOLOGY BULL. 201

Objectives and Contents marine together with Franciscan rocks). In each case, the color used for the unit is the color of the first indicated symbol, which Ideally, the geologic map represents the various features that suggests the more likely or more predominant unit of the combi- one would find on a visit to any locality on the map. Of course, nation. the amount of detail that can be depicted is limited by the scale, In editing the final map, the writer tried to keep in mind not but the most important geologic features are portrayed. During only the large-scale features that illustrate the geologic frame- the compilation this factor was continually kept in mind; where work of the state and that should be apparent even when viewing necessary, particularly significant geologic features, even if the map from a distance, but also to retain important details for small, were exaggerated in order to portray them. Likewise, in which the state is noted, and which can be seen on close in- some places the geology is generalized in order that the most spection of the map. important features are not lost in a maze of detail. The geologic map of the state is first and foremost a factual documentation of Compilation Method the distribution of rocks in the state; it is secondarily an indicator of the presence of major folds and faults where known. As such, For those who may be embarking on their own statewide the Geologic Map of California should be the kind of data source geologic map compilation, and for those who are interested, the that can be used to build theory as closely grounded in reality method used in compiling and pubhshing the Geologic Map of as possible. California will be described. There are probably as many meth- Although the Geologic Map of California confines itself with- ods of compiling as there are compilers, each method having its in the political boundaries of the state, during its construction own advantages and disadvantages. The method described here, attention was given to the geologic data for adjacent areas pro- devised through trial and error, was found suitable for our pur- vided by maps of Arizona, Oregon, Nevada, and Baja California. poses. The method essentially consists of six steps in compiling In the Pacific Ocean area, the map does not attempt to show followed by two steps for publication outlined as follows; geologic units (largely because of the unavailability of data).

However, the major offshore structural features are shown. Data 1. Search and collection of source data. on offshore faults and folds are rapidly accruing, due largely to 2. Evaluation and generalization of data. the increasing efforts by the U.S. Geological Survey and certain 3. Reduction to the compilation scale. universities and other institutions. Unfortunately, the wealth of 4. Plotting on the master base. offshore knowledge possessed by the petroleum exploration com- 5. Further generalization and editing. panies is largely unavailable. 6. Review and correction. 7. Preparation of printing plates. 8. Final proof and publication. Representation of Faults 1. Search and collection of source data: No compilation is The location of faults shown on the Geologic Map of Califor- better than the sources upon which it is based. For this reason, nia are the same as those shown on the Fault Map of California, a large amount of the effort involved in a good compilation is but the faults are not color-coded according to recency of move- spent searching out the best available data. We in California are ment. Thus, all faults on the Geologic Map are shown as black fortunate to have a data bank of map sources going back many hnes, and no distinction is made between historic. Quaternary, years. This data bank was started in the 1930s by Dr. Olaf P. or pre-Quatemary faults. The symbology showing sense of Jenkins, Chief Geologist of the Division of Mines, who came to movement on faults is the same for both maps: pairs of half- the Division in 1929 to prepare a new geologic map of California. arrows for direction of lateral displacement along a fault, arrows Much of the data contained in Dr. Jenkins' collection of maps showing direction of dip of a fault plane or fault surface, and has been superseded by more detailed work, but certain data, letters U and D for relative up and down movement along a fault. especially unpublished data covering remote areas of the state, are still useful or valuable for their historical content. When the preparation of the 1:250,0(X) scale Geologic Atlas Representation of Contacts of California was undertaken, the files of Dr. Jenkins were reor- ganized into r X 2° units, corresponding to the atlas sheets, and All contacts between map units are shown on the Geologic each piece of information was evaluated and either saved or Map of California as solid fine lines except where the map units rejected. As new data were acquired, they were systematically are bounded by faults (depicted by a thicker line), regardless of added into the collection. By 1973 the data bank had expanded the rehability of the contact on the original data source. The from less than a single five-drawer file cabinet to six such cabi- reader is referred to the 1 ;250,0OO scale Geologic Atlas or to the nets and a number of roll-map files—and it is still growing. Then, original source data (indexed in Appendix D) for details as to as now, the amount of new data generated every year was so the nature of the various contacts. great (and becoming greater each year—see Figures 1 and 2) In several places in the Coast Ranges where "Franciscan me- that even a brief suspension of data gathering would seriously lange" is depicted, there may be no contact between it and the compromise the usefulness of the data collection. "undifferentiated" Franciscan Complex because of incomplete In order to ensure completeness in gathering published data, knowledge of the area. In such places the pattern alone separates one can refer to source indexes such as that published by the U.S. "melange" from undifferentiated Franciscan. Geological Survey (Boardman, 1952). However, we found that In a few places where mapping or paleontological control is the published indexes lagged far behind publication of new data. inadequate to distinguish between map units of similar rock Thus, we had to develop our own indexes, and considerable time types, a combination map symbol has been used. For example, and effort were expended in this direction (see Strand and oth- there is shown on the map in the northern Coast Ranges, E-Ep ers, 1958; Koenig and Kiessling, 1968; Kiessling, 1972; and (Eocene-Paleocene marine undifferentiated); in the southern Kiessling and Peterson, 1977). Coast Ranges, Ku-Ep (Upper Cretaceous-Paleocene marine un- We found the largest source of unpublished geologic map

-|- differentiated) ; and on Santa Catalina Island, M KJf (Miocene information on California in universities and colleges, in the .

1985 TEXT TO ACCOMPANY THE FAULT AND GEOLOGIC MAPS OF CALIFORNIA 57

form of theses and dissertations for advanced degrees—especial- surface of the tracing. The negative is then used to photograph- ly in the fields of geology, seismology, paleontology, oceanogra- ically print a positive image on sensitized drafting film. At the phy, geophysics, and geochemistry. Here too, no complete or same time the image is enlarged to the precise size indicated by up-to-date indexes existed, and much time was spent in prepar- the bar-scale shown on the tracing. ing our own indexes and gathering the data (see Jennings and 4. Plotting on the master base: The master compilation base Strand, 1963; Taylor, 1974; Peterson and Saucedo, 1978). map must be scale-stable material. This is absolutely essential in Other unpublished sources of information include oil com- the publication process following the completion of the compila- pany and mining company maps. However, little surface map- tion. The base map shows at a minimum the roads, railroads, ping is done in oil exploration today—the bulk of the effort going streams, lakes, and topographic contours. These features are into subsurface interpretations. The numerous surface maps ex- printed on the reverse side of the base so that any erasures or isting in the older files of oil companies were occasionally used, changes in the geologic compilation will not destroy the base but all too often gaining access to them was difficult or impossi- map features. Showing the culture and topography in one color ble. Moreover, there was no way to know whether data for and the streams and lakes in another makes it easy to distinguish certain areas even existed in company files between the two while plotting the geology. The geologic con- Maps by mining companies consist mostly of underground tacts are then drawn onto the master base utilizing black draw- workings. Often their areal coverage is so narrow as to be of ing ink and technical pens. A fine point is used for normal limited usefulness for regional compilations. However, regional contacts and a broader point for fault contacts. mining exploration maps have been made for remote areas where Invariably additional generalization and simplification are re- mineral deposits occur, and these maps can be very useful. When quired at this stage. Now that these data have been reduced to such maps were known to exist and to be available, they were the actual publication scale, it is possible to visualize the final used. product and to begin generalizing the data. The compiler's objec- One other source of valuable unpublished data is work under tive is, of course, to present a picture that is as definitive as way, especially work that is nearly complete. Numerous maps of possible and that has both clarity and intelligent emphasis. To this kind were made available by the U.S. Geological Survey, the reach this goal, the compiler usually must make compromises Division of Mines and Geology, other state or federal agencies, dictated by the limits of space and legibility. Often the compiler and universities. finds that he has more geologically significant features to portray than space on the map to portray them, and he will have to 2. Evaluation and generalization of data: Oftentimes more choose what to show and what to leave out, relying on his than one interpretation of the geology of a given area exists, and interpretation of the relative importance of the available data. the compiler must choose which to use. Usually, the most recent

is the premise that the geologist has made use of map chosen on 5. Further generalization and editing: After each of the indi- pre-existing data and has correspondingly improved on that vidual reduced segments have been plotted and such inevitable is always. body of information. This usually the case, but not The problems as "dangling contacts" and mismatches have been re- area of geologic interest or the objectives of later mappers may solved (perhaps by consultation with the individual geologist, by different the earlier workers, and deliberate have been from compromises, or by field examination), the map is ready for an The compiler must omissions in their maps may have been made. overview evaluation. At this point, attention is given to such for possibilities. always be on the lookout such factors as balance (areas where too much detail is shown), clari- evaluated, tracing of the After the data have been a mapped ty (taking a more detached look at the overall map), and empha- area is for inclusion into the compilation. The tracing is made sis ("can't see the forest for the trees"). A most useful aid at this overlay of either good-quality tracing vellum or done on an step is the preparation of a hand-colored copy of the map. This polyester film. advantage of using drafting film is drafting The may be a long and exacting task, but its value cannot be overesti- with- that, with its superior transparency, it can be seen through mated. With a hand-colored map, consideration of the above out the a light table. Drafting film, of course, is also use of mentioned factors is greatly facilitated and many problems scale-stable. The original mapped units are combined according become glaringly apparent. to a predetermined legend, and the contacts are then generalized in accordance with the amount of reduction that will be required. 6. Review and correction: Before the compilation is submitted

for publication, it is advisable to have the map reviewed by 3. Reduction to the compilation scale: The tracings of the experts conversant with wide areas of regional and detailed geol- combined and generalized units are marked with a bar-scale ogy of the area. During preparation of the Geologic Map of showing the amount of reduction required to fit the master base Cahfomia, we were fortunate to have the benefit of extensive map. A few major roads, or intersecting latitude and longitude reviews by a wide range of professionals affiliated with the U.S. lines, are drawn on the tracing in order to verify the amount of Geological Survey, and universities, other State of California and reduction or to provide control for adjusting any distortion that Federal agencies, as well as a number of consulting geologists might exist in the source map. The tracings are then photograph- and firms. Each reviewed our maps with great interest and dedi- ically reduced to accurately fit the compilation base map. For the cation. Geologic Atlas, reduction was made to the final publication Following the review process, the various comments, correc- scale, that is, 1 :250,000. In prepanng the 1 :750.000 scale Geolog- tions, and suggested additions are evaluated and the necessary ic Map of California, intermediate - scale work sheets at 1 :250,- changes incorporated in the master compilation. 000 scale were prepared and later reduced to the 1:750,000 publication scale. 7. Preparation of printing plates: After the map compilation

The photographic reduction technique used most successfully is submitted for publication, it becomes a job for the drafting and efficiently by the Division was performed by high-quality staff and lithographer. However, the responsibility for checking engineering reproduction firms equipped with large cameras, the work submitted to the lithographer still falls on the compiler. vacuum frames, and photographic processing labs. The proce- Inevitably, no matter how carefully the compilation has been

dure for this technique consists, first, of making a 105-mm nega- prepared, problems will be encountered which only the geolo- tive of the tracing, utilizing a vacuum frame to ensure a fiat gist-compiler can resolve. —

58 DIVISION OF MINES AND GEOLOGY BULL. 201

It is usually beyond the knowledge and experience of the subdivisions within epochs or periods; for example, Miocene geologist-compiler to tell the drafting staff how to make the map marine sedimentary rocks are shown rather than uppei, middle, ready for the printer. However, the compiler should understand and lower Miocene marine sedimentary rocks. Table 10 illus- something of the printing procedure in order to recognize some trates how the units of the 1:250,000 scale Geologic Atlas of of the problems in preparing the printing plates. A summary of California have been grouped into the new 1:750,000 scale Geo- the steps involved in this procedure is as follows; First, the logic Map of California. compilation must be photographically transferred to a sensitized From Table 10, it might appear that the units shown on the drafting film in order that the contacts and faults can be scribed map are defined by time lines, but they are in fact drawn on (engraved). These are first scribed solid so that the necessary formation boundaries. For convenience, formations of approxi- "peelcoats" for each of the formation colors and patterns can be mately the same age and origin are grouped under the same made by the lithographer. Then the contacts and faults, which symbol. Thus, all the marine formations of Miocene or predomi- were scribed as solid lines, are "dashed" where required by nantly Miocene age are shown as "M," and all the volcanic rocks opaqueing, usually utilizing a "visitype" pattern on a transparent of Miocene or predominantly Miocene age are shown as "Mv." overlay sheet. Similarly, overlays are prepared using "visitype" Although the boundaries shown on the map are drawn on the for dotted faults, queried faults and queried contacts, thrust fault basis of mapped formations, only the Franciscan Complex is "barbs," fault attitudes, formation symbols, volcano symbols, separately identified. This exception is warranted because of the fault names, hot springs and well locations, and any other special Franciscan's widespread extent, its time span of deposition (Ju- symbols. Some of these symbols can be combined on the same rassic through Cretaceous), and its importance in the under- overlay, but usually certain ones are kept separate if the map is standing of California geologic history. to be printed in various forms for other purposes where simplica- For reference purposes, a complete listing of all formations tion may be required or different colors are to be used—for grouped within each of the units shown on the Geologic Map of example, color-coded faults for a fault map and uncolored California is included in Appendix C. The Geologic Legend of (black) faults for a geologic map. Lastly, an overlay for the the map contains brief descriptions of the units indicating the explanation, titles, and other peripheral data is prepared. predominant lithologic types. Among the Cenozoic rocks, a The plates and overlays of the contacts, faults, and the forma- statement is also included to indicate the degree of consolidation. tion symbols are then photographically combined, and a film This could be useful in estimating relative slope stability, ground positive is made of the combination. Ozalid prints of this com- shaking during earthquakes, erosion resistance, and liquifaction posite plate are made, and these are hand-colored for use as color potential. guides by the lithographer when the peelcoats are made. The plan for classification of the rock units in the Geologic Legend, which is reproduced in Figure 15, follows a systematic 8. Final proof and publication: After all the necessary scribed scheme. The rock units have been broadly classified into sedi- plates and overlays are prepared, the hand-colored guides made, mentary, volcanic, metamorphic, and plutonic lithologic groups, and a color and pattern scheme selected, the "map" is ready to and are arranged in normal stratified sequence with the oldest send to the lithographer. In addition to the above, a dummy rocks at the bottom of the chart. Thus, the relative and compara- layout is included, together with instructions concerning the ble ages among the lithologic groups are indicated as closely as various plates for the base map (previously acquired from the possible—rocks of approximately the same age being shown on U.S. Geological Survey). After these materials are sent to the the same horizontal level in the legend. The marine and nonma- lithographer, the job for the compiler and drafting staff does not rine (continental) facies of the Cenozoic sedimentary rocks have end, because the extremely important task of proofing is yet to also been distinguished. come. The Cenozoic rocks, ranging in age from Holocene through

After the lithographer prepares the printing plates, the first Paleocene, have been grouped into: ( I ) marine sedimentary color proof will arrive. The compiler will be especially interested rocks, (2) nonmarine (continental) sedimentary rocks, (3) vol- in seeing how the selected color scheme appears. Do the colors canic rocks, and (4) plutonic rocks. The nonmarine sedimentary show up properly? Can units be adequately distinguished? Are rocks are distinguished from the marine rocks by the letter "c" the color shades aesthetically pleasing? Changes in colors or for example, "Pc" for Pliocene "continental" rocks. The Ceno- patterns may be required before the second proof is prepared. zoic volcanic rocks have been further subdivided into fiow rocks The drafting staff, in the meantime, will make a careful, sys- and pyroclastic rocks, the pyroclastic rocks being distinguished tematic search for printer's errors in the placement of colors by the superscript "p." and/or patterns. Everyone, of course, will be interested in how The lower half of the Geologic Legend, representing the pre- the layout appears, the titles, explanations, and legend. After all Cenozoic rocks, is more complex and includes rocks of Precam- the discovered errors have been noted, and instructions to the brian through Mesozoic age. These are grouped into: ( 1 ) marine lithographer for any changes in color and layout have been sedimentary and metasedimentary rocks, (2) mixed rocks (of made, the lithographer will correct and change the printing uncertain age, consisting of undivided granitic and metamorphic plates accordingly and a second proof will be prepared. This rocks or undivided metasedimentry and metavolcanic rocks), procedure will be repeated until satisfaction by all concerned is (3) metavolcanic rocks, and (4) plutonic rocks. attained. The map is then ready for printing. The plutonic rocks are classified by age and by broad litholog-

ic types. For example, the granitic types are the most common in California and are the most amenable to classification by age (mainly on the basis of radiometric data). Among the granitic Classification of Rock Units and rocks, the Mesozoic ones have the greatest extent, but Precam- Special Problems brian. Paleozoic, and Cenozoic granitic rocks are also distin- guished. These are all identified by the symbol "gr" indicating The rock units selected for the new Geologic Map were largely their basic composition, and the superscripts Mz, pG, Pz, and Cz derived from the legend for the 1:250,000 scale atlas sheets. The are used to indicate their age. Other major plutonic types are 124 units shown on the 1:250,(XX) scale series have been com- separately identified but not subdivided in detail. For example, bined into 52 units. Fewer units are used as a result of fewer the ultramafic rocks (mostly serpentine) are shown as "um" and 1<)85 TEXT TO ACCOMPANY THE FAULT AND GEOLOGIC MAPS OF CALIFORNIA 59

Atlas

on

:250,000

Geologic Units 1

10

O °^

z 5 O > 60 DIVISION OF MINES AND GEOLOGY BULL. 201

CO u O

z < X men. Si z < < um U t z u < OM o mz U y z o t-

o 1985 TEXT TO ACCOMPANY THE FAULT AND GEOLOGIC MAPS OF CALIFORNIA 61

gabbroic rocks as "gb." The ultramafic rocks in large part are stratigraphic position, the unit is depicted on the map by the

fragments of mantle material of various ages and rest in their symbol representing the geologic period when it was deposited.

present position by tectonic rather than by magmatic processes. If the age of a metamorphic rock unit is uncertain or unknown, Rocks of the Franciscan Complex have been separated into we tried to show the rocks by their characteristic field appear- three subdivisions. "KJf" is the most widespread, and consists ance, for example, "sch" (schist of various types) or "Is" (mar- of Cretaceous and Jurassic sandstones with smaller amounts of bleized limestone or dolomite). Where undivided pre-Cenozoic shale, chert, limestone, and conglomerate. "KJf„" indicates metamorphic rocks have not been mapped by their metamorphic Franciscan rocks that have been intensely fragmented and characteristics, they are shown on the compilation simply as sheared into a melange . "KJf," is the designation for the meta- "m" (undivided metasedimentary and metavolcanic rocks), or morphosed part of the Franciscan Complex, consisting largely of "mv" (metavolcanic rocks). Where the general age of some

blueschist and semi-schist. metasedimentary and metavolcanic rocks is known, the symbols A hybrid symbol "SO" is used for Silurian and Ordovician "Pz," "Mzv," and "Pzv" are used to indicate Paleozoic rocks. These rocks are found in California in limited extent and metasedimentary rocks and Mesozoic and Paleozoic metavol- could not be readily portrayed on the present map if shown canic rocks. separately. The rocks occur in narrow bands in the Klamath The map legend also shows that the Geologic Map of Califor- Mountains, Sierra Nevada, and Basin Ranges geologic prov- nia tends to emphasize bedrock rather than surficial geologic inces. units. It can be seen, however, that various surficial deposits of Because in many places in California the older rocks are de- Quaternary age are lumped into the unit "Q." The largest area void of fossils (or the forms found may not be complete enough of such surficial deposits in the state is the Great Valley of or diagnostic of age), several broad rock groups have been desig- California. Smaller deposits occur elsewhere, but they are usu- nated for some of the pre-Cenozoic rocks. For example, the ally shown only where the area covered is significant. Stream symbols "m," "mv," "gr-m," "sch," and "Is" have been used for alluvium, fan deposits, salt deposits. Quaternary lake deposits, rocks whose ages are very uncertain. The symbol "m" is used for and Quaternary marine or stream terrace deposits are all includ- undivided pre-Cenozoic metasedimentary and metavolcanic ed in the unit "Q." Such deposits, however, are not shown if they rocks; "mv" for undivided pre-Cenozoic metavolcanic rocks; greatly interfere in the depiction of the bedrock units. An excep- "gr-m" for a mixture of granitic and metamorphic rocks ranging tion to this general rule is the case where a fault intersects or in age from Mesozoic to Precambrian; "sch" for schist that is offsets Quaternary surficial units. In such cases, the young surfi- believed to be mostly Paleozoic or Mesozoic (although some cial unit might even be exaggerated to illustrate this important may be Precambrian); and "Is" for hmestone, dolomite, and evidence for recency of faulting. marble of various pre-Tertiary periods or of uncertain age. Certain other Quaternary surficial deposits are shown where A similar broad rock unit group has also been used in one significantly large. For example, glacial deposits are shown be- instance in the Cenozoic section. This is the symbol "Tc," which cause of their importance to Quaternary chronology, and exten- is used to represent nonmarine sedimentary rocks whose relative sive dune sand deposits are depicted, especially where they occur age cannot be determined any closer than Tertiary. as rather large areas of possible economic or geomorphological

Special problems exist in the Cenozoic rocks where it is impor- importance. Lastly, some Quaternary landslide deposits are in- tant to separate the nonmarine from the marine sedimentary dicated where they are particularly large (for example, Black- rocks. The marine Tertiary rocks lie principally along the west- hawk and Martinez Mountain rock slides in southern em part of the state (coastal ranges). However, in many places California), or where they drastically obscure the geologic rela- within sections of shallow-water marine rocks, there are nonma- tionships of the bedrock units (for example. Table Mountain rine strata—for example, rocks containing coal or hgnite, red serpentine landslides in the central Coast Ranges). Unfortunate- beds, and sand dunes. These are not shown as nonmarine units ly, the decision to show landslide deposits was not made until the if they appear to be very local or limited in area. Likewise, many compilation was well underway; as a result, some truly huge elevated marine terraces are covered wholly or in part by a thin landslides have not been depicted. This is not altogether a short- cover of nonmarine talus debris. These areas also are generally coming of the map, however, because if too many large land- shown as marine to emphasize the geomorphic origin of the unit. slides were shown, the bedrock geology would be Similarly, a unit like the Sespe Formation, which consists correspondingly obscured. predominantly of red beds and other nonmarine deposits, does have marine facies—particularly as the unit is traced westward toward the sea. The Sespe, in addition, poses a problem because its age ranges from late Eocene to early Miocene. In portraying Colors, Patterns, Symbols of Rock Units, this unit, a compromise has been chosen, and the unit is shown on the map by its predominant characteristics—nonmarine and Map Appearance Oligocene. Among the older (pre-Cenozoic) rocks, the nonmarine facies A combination of colors, patterns, and symbols has been used are usually almost impossible to recognize as mappable units and to distinguish the rock units shown on the Geologic Map of have only been done so in a few places in California. For exam- California. Each device was chosen to adhere as closely as possi- ple, the Cretaceous Trabuco Formation and the Carboniferous ble to national or international convention and to best illustrate Supai Formation have been recognized as being wholly or in part the complex geology of California. of nonmanne origin. However, these rocks are exposed only in limited areas in California, and are hence grouped on the 1:750,- I . Colors: Worldwide efforts to achieve a systematic scheme 000 scale map with the marine units. of colors for geologic maps began nearly a century ago. The 2nd Metamorphic rocks were the most diPTicult to denote on the and 3rd International Geological Congresses made recommen- Geologic Map of California. In general, the older rocks show dations for international standards in 1881 and 1885, and the increased evidence of metamorphism, although this might be of World Map Commission made certain modifications in 1958. In a very low grade. Where the age of metasedimentary rocks is this country, attempts to set a national standard of colors for known, for example, by their fossil content or by well-defined portraying rocks of each geologic age began in 1881 with J.W. 62 DIVISION OF MINES AND GEOLOGY BULL. 201

GEOLOGIC

MARINE SEDIMENTARY ROCKS NONMARINE (CONTINENTAL) SEDIMENTARY ROCKS 1985 TEXT TO ACCOMPANY THE FAULT AND GEOLOGIC MAPS OF CALIFORNIA 63

LEGEND

\ OLCANIC ROCKS PLUTONIC ROCKS

0.. a

0>: R«c«At (Holocan*) dconk flow tocki; nMwr pyrodoftk dapoiiti (>*: t«c««l (Holocana) pyrodoitk and loiconk mudflow 6*poun.

a,'

dcpotiH.

Ov* : Q\iat**norf pyrodoiHc and vokonk mvdflow dvpoftv

Tv : Tsrtiofy volcomc flow rockt; minor pyrodaiHc

r.»i T«ft»ory pyroclaihc of>d vokontc mudflow dvpoiitt.

OH^

Tvftiory mtrvvv* rocki; moitty ihoNow (hypobytiol) C«nozo*C (Tertiary) Qronilic rock*—quartz monxo- plugi and dikvi. nile, qwortz lotit*, ond minor monzonlte, orar>odior- it«, ar>d gronitv; found m ttte Kingilon, Ponomint. AmorgoMi. and G'e*nwot»r Ror>oet in K>urt>«Oit- em Cal'pfomta

MIXED ROCKS META\OLCANlC ROCKS PLUTONIC ROCKS

Uf

Urtdivided Metoioic volconic or»d metovokonic Mesozok granite, quortz monzonite, granodiorite, rockt Andeiile and r+iyoJit« Bow rocki. greenilone, ond quart! dionte

TolconK breccia ond other pyrockjltic rocki; in port itrongfy melomorphoied Includei vokonic rocki of Fronc'Kon Complei- boMiltic pillow lovo, diaboie, greenitorte. artd mir>or pyrocloitic rocki. Ultromofk rockl. mottty Mrpentirte. Mirtor pendo-

tite. gobbro, ond diobai* Otieffy Metotok

GroniHc and NMtamorpluc rocks, mosriy gn«iu and Gabbro artd dork (fioritk rocki; chiefly Mewzok. oftwr rwtamorphk rockl iniected by gronitic rockv MeioioK h) pTtcomhnan,

Undated gronitk rocki. Undnnd*d pre-Csrtozoic mctascdimen lory ond Undnrided pre-Cenozok metovolconic rocki. ln< m«tovolcan>c rocki o4 grval vonety Moitty Uote. cli>dei latite, docite. twtf. and greenstone; common- qwartiii*. Komfeli. chert, phyllite. myionil*. icKiit, ly KhiltOM

gr>*

Ufxlivided Paleozoic metovokonic rockt Moitly Paleozok ond Permo-Trioiiic gronitk rockt in the fkiwi. breccia, and tuM. irKluding greenstone, dio- Son Gabriel ond Klamath Mountomt. boM ond pilow lovQi; minor mterbedded ledimert-

oO:

CompU* of Precombrion igneout ortd mclomorphK Precombnon gronde. tyer^ite. orvorthotile. artd rockL Mottly gn*>u and Khiil intruded by igrkeoMt gobbroK rockt m Itte Son Gobnel Mountomt. atio rockij noy be Mvtoxok in port. vorioui Precombnon pKttonk rockt eliewhere tn towtheottem CoTifomio. 64 DIVISION OF MINES AND GEOLOGY BULL. 201

Table 11. Comparison of "American" and "International" map colors for sedimentary rocks.

SYSTEM 1985 TEXT TO ACCOMPANY THE FAULT AND GEOLOGIC MAPS OF CALIFORNIA 65

Powell, Director of the U.S. Geological Survey. For an interest- shown as Franciscan on some maps) are now known to contain, ing history of the development of schemes for geologic map in the sparse fossil record, early Tertiary microfossils. Hence, colors, the reader is referred to King and Beikman (1974, p. these rocks, too, are shown as a transitional green between the 25-28). Lower Tertiary and Upper Cretaceous colors. Likewise, lithol- Both schemes proposed that the orderly sequence of sedimen- ogy and other characteristics of Miocene and Oligocene marine tary rock units be portrayed on geologic maps by a prismatic sedimentary rocks are often very close and hence are portrayed sequence of colors. For example, with the use of yellow, green, by similar colors on the map. blue, and violet, yellow would be younger than green, green younger than blue, and so forth—the darker shades representing 2. Patterns: In addition to colors, certain rock units are distin- progressively older rocks (Table 11). In this way, the map would guished by an overprint pattern (Table 13). Basically, all marine show at a glance which sedimentary rocks were younger and sedimentary or metasedimentary units, whether Cenozoic, which were older, and oftentimes, the structures they form Mesozoic, Paleozoic, or Precambrian, are represented by solid would be readily apparent. colors without any overprint patterns. Nonmarine units (distin- In actual practice, most geologic maps follow this principle guished on this map in the Cenozoic only) are shown by the but with departures because of limitations in contrasting shades same color that is used to show their marine counterparts, but of color for areas with numerous units of comparable ages. The with a stipple pattern overprint (either blue or red, depending "International color system" works well for maps of Europe on which shows up better).

(where the system was proposed), but it has important deficien- cies for geologic maps of the United States. The international Table 13. Patterns used on Geologic Map of California. scheme, unfortunately, is not entirely suitable for areas where Paleozoic and Precambrian rocks predominate and where they UNIT have been subdivided into numerous periods. This was not a problem in Europe where neither the Precambrian nor the Paleo- zoic is extensive or subdivided as much as in some other parts of the world. Therefore the map colors proposed by Powell, with subse- quent elaborations, have become the "American color system," which is the general model used by the U.S. Geological Survey. The principal differences between the "American" and "Interna- tional" color systems are shown in Table 1 1 for the sedimentary rocks and Table 12 for the igneous rocks. Note that in the' Ameri- can" system the blues and shades of purple extend farther down in the Paleozoic Era, and also note the different treatment of the intrusive and extrusive rocks. The color scheme chosen for the Geologic Map of California is largely patterned after the "American" system, as exemplified by the U.S. Geological Survey's Geologic Map of the United States (King and Beikman, 1974) for the sedimentary rocks, but a closer adherence to the "International color system" was fol- lowed for plutonic and volcanic rocks. Note that bright reds and purples have been reserved on the California map for plutonic rocks. This departure from the "American" system is in keeping with a long tradition of geologic maps of California. The use of bright colors for the plutonic rocks achieves a much better con- trast between the vastly different sedimentary and plutonic rock types. A glance at the Geologic Map of California and the bright red color immediately conveys the location of batholithic rocks, and the deep purple color shows the distribution of serpentinite and related ultramafic rocks, which are so important tectonically and economically to California. Following the use of intense red for the deep-seated plutonic rocks, warm shades of pink and orange are used to portray volcanic rocks. Among the prismatic colors used to portray sedimentary rocks, there is not a large contrast between the yellowish-greens of the Lower Tertiary rocks and the light green of the Upper Cretaceous rocks. This was done purposely, because in many places in California the distinction between rocks of these ages is very difficult to draw. Lithologically, the rocks of these two ages are commonly identical, and the lack or sparseness of fossils makes the separation in many cases almost impossible. A similar situation exists with the "coastal belt" rocks of northwestern California, shown as "TK." These rocks of li- thologic similarity* to the Franciscan Complex (indeed, often

* Cottstal belt rocks, when analyzed carefully, often have a high K-feldspar content, unlike the typical Franciscan rocks. .

66 DIVISION OF MINES AND GEOLOGY BULL. 201

Symbols become increasingly useful as the map fades with time same color. In this way, they may appear as one unit from a and makes some color contrasts more difficult to distinguish. We distance and the major sedimentary groups are emphasized; have also found it particularly useful to label every area bounded however on closer inspection, the rock groups can be separated

by contacts with a symbol because it enables the pubhcation of by the more subtle color contrasts. an uncolored edition of the geologic map. The letter symbols used on the Geologic Map of California were chosen to comply as much as possible with accepted con- Geologic Time Scale ventions, and also to be simple. Most symbols consist of a single capital letter indicating the geologic epoch or period when the In addition to the conventional geologic legend on the Geolog- ic of California, rock tormation was formed. In some cases, combinations of Map in the lower left-hand part of the map is a chart portraying capital letters were used where the age of the unit widely trans- a generalized geologic time scale. This chart is reproduced as Table 14 gresses geologic time, for example, "TK" for Tertiary-Cretaceous (but without color). rocks. Likewise, "SO" was used for Silurian and Ordovician The purpose of this generalized time scale is to assist those rocks, which because of their limited exposure in California, who are not familiar with the geologist's way of depicting rela- would not have shown up individually. tive rock ages. The term "relative geologic time" is used on the Because of the repetition of certain first-letters in the names chart, for that is how geologists began scores of years ago to of several periods and epochs, a number of contrived symbols depict rock sequences, not knowing the rock's actual age in were utilized. For example. Pliocene, Paleocene, Permian, and numbers of years. Of course, with the knowledge of radioactive Paleozoic, each begin with the letter "P"; therefore, the follow- decay rates and other sophisticated dating techniques, geologists ing symbols were used for these units respectively; P, Ep, Pm, and now can determine the actual age of many types of rocks. Pz. This follows the convention used for many years on the However, the generalized geologic time scale was devised to put Geologic Atlas of California and on some U.S. Geological Sur- rock ages in some sort of perspective, especially as they relate to vey maps. Cenozoic, Cretaceous, Carboniferous, and Cambrian the evolution of life on the planet. The same geologic time scale is used universally by all geologists paleontologists. also posed a problem with the repetition of the first letter "C." and This was resolved by using the symbols Cz, K, C, and €. This The generalized time scale shown on the Geologic Map of has also been common practice on Califomian, U.S. Geological Cahfomia is shown in color to match the major time units of the stratified rocks depicted the Subdivisions Survey, and a number of foreign geologic maps for many years. on map. of the various Lower case "u" and "1" differentiate upper and lower parts of periods are, of course, shown on the Geologic Map by shades of the colors on the generalized certain periods, for example, Ku and Kl. Lower case "c" identi- shown geologic time scale. For example. Upper and Lower Cretaceous are in shades fies nonmarine ("continental") sedimentary rocks. A lower case shown of green, and subdivisions of the Paleozoic are in shades "v" is used to denote volcanic rocks, and a superscript "p" is shown of blue used to distinguish Cenozoic volcanic rocks of pyroclastic origin and lavender. colored time scale from flow rocks. Other lower case modifiers used are; "g" for The shows that the colors are arranged as a spectrum with yellow for the Quaternary glacial deposits (Qg), "i" for Tertiary intrusive youngest rocks, green for Meso- rocks (Ti), and "s" for extensive Quaternary sand deposits zoic.and blue and lavender for Paleozoic. Thus, the map-user can (Qs). quickly get an approximate idea of the distribution and age of stratified rocks the state. For plutonic and metamorphic rocks that range widely in age within or are of uncertain age, lower case letters or combinations of letters are used to indicate their broad rock classification. For Volcanoes example, "m" is used for undivided pre-Cenozoic metamorphic rocks (where metasedimentary and metavolcanic rocks have not The location of numerous volcanoes of all types (cinder cones, been distinguished); "mv" for metavolcanic rocks; "sch" for domes, composite or stratovolcanoes) are shown on the Geolog- schist; "Is" for hmestone, dolomite, and for granitic marble; "gr" ic Map of Cahfomia with the conventional volcano symbol, in rocks; "gb" for gabbro; and "urn" for ultramafic rocks (mostly the same way that they are shown on the Fault Map of Cahfor- serpentmite and related rocks). nia. Some 565 volcanoes are plotted, most of which are cinder cones. The greatest concentration of volcanoes in California are 4. Map appearance: It is apparent, even from a distance, that in the Modoc Lava Plateau, Clear Lake, Owens Valley, and the Geologic Map of California shows a major color contrast certain southern California desert areas. For more discussion of among certain geologic units. This was purposely intended. For volcanoes, see pages 43 - 45 example, the deep-seated batholithic-type rocks shown in bright red hues are easily distinguished from the paler (pastel) hues depicting the sedimentary and metasedimentary rocks (arranged Batholiths and Plutons in a prismatic sequence, yellows through lavender with the dark- er colors being the oldest). Between these two principal color Numerous granitic intrusive bodies are found in California, and rock contrasts are depicted the Cenozoic volcanic rocks, and many of these have been given specific names as they are shown in shades of warm pink and orange. Thus, at a glance, the studied in detail. Table 15 is a list of all the named granitic map user is able to see the distribution of the granitic rocks, the intrusive masses shown on the Geologic Map of California, 1977 widespread Cenozoic volcanic rocks, the sedimentary and edition. Additional plutons have been carefully studied and metasedimentary rocks, and the vast basins of unconsolidated named, but because of their relatively small size or the lack of alluvium. space available on the map, they are not labeled. Others have On closer inspection, with attention to various patterns used, been the subjects of careful study, but the results of the studies the map-user is able to easily differentiate between marine had not been published at the time the compilation of the map and nonmarine rocks (stipple pattern on the latter); most vol- was under way.

canic rocks (random v-pattem) ; and metamorphic rocks The term hatholith has traditionally been used for large plu- (randomly-oriented dash pattern). In addition, stratified rocks of tonic bodies, usually of granitic composition, that generally similar age and lithologic origin appear as different shades of the cross-cut the structure of the rock they intrude and have steep 1985 TEXT TO ACCOMPANY THE FAULT AND GEOLOGIC MAPS OF CALIFORNIA 67

Table 14. Geologic time scale.

RELATIVE GEOLOGIC TIME TIME

in millions of TIME OF APPEARANCE 0(^ DIFFERENT FORMS OF LIFE Epoch years before present

1 Historic record in California, 200 years

Post-glacial period Quaternary

Ice oge, evolution of man.

Age of mammotfts.

Spreod of onlfiropoid apes.

Tertiory Oligocene Origin of more modern families of mammals, grazing animals.

Origin of many modern families of mammals, giont mammals.

Origin of most orders of mammals, early fiorses.

Appeoronce of flowering plonts; extinction of dinosaurs at end; appearance of few modern orders Cretaceou! a and fomilies of mammals.

Appeoronce of some modern genera of conifers; origin of mommols and birds; fieigf>t of dinosaur evolution.

Dominance of mommol-liko reptiles.

225 -

Appeoronce of modern insect orders.

280 •

Dominance of omphiblans and of primitive tropical forests wfiich formed coal; earliest reptiles. Carboniferous 320 Systems Earliest ompftibions. 345

Earliest seed plonts; rise of bony fisfies.

Siluric Earliest land plants.

Earliest known vertebrates.

Appeoronce of most phyla of invertebrates.

Origin of life; olgae, worm burrows. Precombrian

4,500 Estimoted age of earth.

Modified from U S. G«olo9icol Survey. Geologic r>Jamei Commitlee, 1972, and G. ledyord Slebbins, ProceHes ol organic evolution, 1966, Prenfice.Holt, Inc., Englewood CliKs. New Jersey

• 11.000 yeofi, Zlony el ol.. 1974, US Geological Survey Mop MF 585,

walls dipping outward so that the body enlarges downward and The terrane shown on the State Geologic Map as the Sierra has no visible or inferred floor. Often a batholith is a regionally Nevada batholith is composed of granitic rocks of various com- extensive complex body, consisting of many individual intrusive positions and is made up of a number of separate intrusive masses of various compositions. The term pJuton is a noncom- masses, the limits of which have often not been delineated. mittal term for an intrusive igneous body of any shape or size. Hence, with the exception of a number of satellitic intrusive Also, it is commonly applied to the various separate intrusive bodies in the northwestern part of the Sierra, the main Sierra masses that make up a batholith. Stock is a much more restric- Nevada batholith has not been separated into its component tive term for an intrusive igneous body having the features of a plutons on the 1977 Geologic Map of California, The batholith batholith, but covering less than 40 square miles (100 km^). has been studied most intensely in the central and northern parts The largest of the batholilths in the state is the Sierra Nevada by the U,S, Geological Survey (for example, Bateman and oth- batholith, which is at least 644 km (400 miles) long and as much ers, 1963; Hietanen, 1973). In general, the major plutons in the as 80-97 km (50-60 miles) wide. Strictly speaking, the Sierra western part of the batholith are older and more mafic than those Nevada batholith is confined to the granitic terrane of the Sierra in the eastern part. Isotopic ages in the Sierra Nevada batholith

Nevada (Bateman and others, 1963), and it is labeled this way range from Late Triassic to Late Cretaceous. on the Geologic Map of California. However, in a broader sense The granitic rocks of the southern California batholith occupy the term has been applied by many geologists to include the Inyo an area about 97 km (60 miles) wide and more than 1610 km batholith and other similar granitic rocks to the east and north, (1,(X)0 miles) long extending from Riverside to the southern tip far into Nevada (Crowder and others, 1973, p, 285 and 287), of Baja California. Although this batholith consists of many 68 DIVISION OF MINES AND GEOLOGY BULL. 201

Table 15. Batholiths, plutons, and stocks identified on the 1977 Geologic Map of California. NAME —

1985 TEXT TO ACCOMPANY THE FAULT AND GEOLOGIC MAPS OF CALIFORNIA 69

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logicol Investigations Mop 1-512. Wright, L.A., 1975, Late Cenozoic fault patterns and stress fields in the Great Basin and westward displocement of the Sierra Nevada block: Geology,

U.S. Geological Survey Stoff, 1971, Surfoce faulting, in The San Fernando, V. 4, p. 489-494. Colifornia, earthquake of February 9, 1971: U.S. Geological Survey

Professional Paper 733, p. 55-76. Yerkes, R.F., 1972, Geology and oil resources of the western Puente Hills area, southern California: U.S. Geological Survey Professional Paper

Vedder, J.G., and Brown, R.D., Jr., 1968, Structural ond strotigrophic rela- 420-C, 62 p. tions along the Nacimiento fault in the southern Santo Lucio Range, and

Son Rafael Mountoins, Colifornia, in Dickinson, W.R., and Grontz, A., Ziony, J.I., and others, 1974, Preliminary mop showing recency of foulting

editors. Proceedings of conference on geologic problems of Son Andreos in coastal southern Californio: U.S. Geological Survey Mop MF-585. PART III APPENDICES

False facts are highly injurious to the progress of science, for they often endure long; but false views, if supported by some evidence do little harm, for everyone takes a salutary pleasure in proving their falseness.

-Charles Darwin

1985 TEXT TO ACCOMPANY THE FAULT AND GEOLOGIC MAPS OF CALIFORNIA 77

APPENDIX A

INDEX TO FAULT NAMES SHOWN ON THE FAULT MAP OF CALIFORNIA, 1975 EDITION

NAMED FAULTS SHOWN previously named fault), warrants a name, if only for con- venience of reference.

A list of all the faults plotted and named on the 1975 edition The name of a geographic feature on or near the fault should of the Fault Map of California follows. Because of space prob- be used to help in visualizing its location or "type locality." lems, not all these faults are named on the Geologic Map of This practice reduces the confusion in nomenclature when California, 1977 edition, although an attempt was made to iden- faults are determined to be connected or separated by fur- tify the major faults on that map. ther studies. The concept of a type locality for faults was first The faults are listed alphabetically, followed by the name of suggested by H. J. Buddenhagen, M. L. Hill, F. S. Hudson, the State Atlas sheet on which the fault occurs. Many additional and A. O. Woodford in 1930 (Bulletin of the American named faults occur in the state, and a good number of these are Association of Petroleum Geologists, v. 14, no. 6, p. 797- indicated on the sheets of the larger-scale Geologic Atlas of 798). Over the years this practice has not always been fol-

California (see supplemental index to fault names, p. 8 ). lowed, but it is strongly recommended that the type locality Many other named faults occur in California, but most of be an integral part of any description of a newly described these could not be identified, even on the Atlas sheets, because fault. The first public description of a fault should include of the lack of space, or because they had not been formally an accurate location of its trace, preferably by an adequate- recognized in a geologic publication. scale map, and a description of its best exposure ("type locality").

PROCEDURE FOR As much information as can be determined about the geom- etry of the fault should be described, including length, direc- NAMING FAULTS tion of prevalent strike, direction and magnitude of dip, and recency of movement as can best be determined. The Of course, as time goes on, more and more faults will be amount of displacement should be given if it can be reason- mapped and described in pubhshed geologic reports. Although ably deduced, with careful attention being given to the dis- no systematic procedure exists for naming faults (such as the tinction between separation and slip, that is, the distinction "Code of Stratigraphic Nomenclature" devised and periodically between displacement between the traces of a displaced expanded by the American Commission on Stratigraphic No- plane on two sides of a fault and displacement of points that menclature as a guide for naming formations and other strati- were formerly adjacent (see J. C. Crowell, 1959, Bulletin of Association of Petroleum Geologists, v. 43, graphic units) , it is important for geologists to exercise judgment the American in devising new fault names. For example, most faults are named no. 11, p. 2653-2674). If not enough of these factors can be after nearby prominent geographic features; this convenient determined, the naming of the fault should perhaps be practice should be continued. A notable exception to this prac- delayed until more is known about it. tice is the recently named Hosgri fault, located offshore near San

Luis Obispo County. The need to name this fault arose when it Previously used fault names should not be used for faults in became a subject of concern during the evaluation of the seismic other areas of the state that might have a similarly named safety of the adjacent Diablo Canyon nuclear power plant. There geographic feature. To do so creates confusion. For example, was no prominent geographic feature noted on bathemetric we have already three "San Jose Faults" in the state, and charts of the faulted area to name the fault after. In this instance, four "Hot Springs faults," two of which are less than 25 it was decided that the two geologists who first published a map miles apart! Even though the following indexes of fault showing the fault should be recognized in the name. Thus, the names are incomplete, they should be consulted, and similar fault became known as the "Hosgri" fault a contraction of the — names should be avoided. As the Division of Mines and first parts of the geologists' names, Hoskins and Griffiths. Geology publishes updated fault maps of the state, it will Although naming faults does not require the kind of care and incorporate new fault names. It would be helpful and it consideration to detail specified for naming geologic formations would ensure completeness if newly described faults are by the "Code of Stratigraphic Nomenclature," a cavalier ap- called to our attention and a description provided to this proach can easily result in subsequent confusion. In order to Division. Such information should be addressed to the atten- avoid confusion, careful consideration should be given to the tion of the State Geologist, California Division of Mines and following principles when naming surface faults. Geology, Resources Building, Room 1341, 1416 Ninth Street, Sacramento, CA 95814. 1. A fault should be given a name only if it has considerable

length or offset, or is situated in hazardous proximity to

man-made structures, or is of recent origin, no matter the In recent years, with the advent of strong earthquakes with length. For example, any future fault rupture associated new (or newly recognized) faults, the intensity of investiga- with an earthquake (if not on a previously recognized or tion has sometimes resulted in different names being applied 78 DIVISION OF MINES AND GEOLOGY BULL. 201

to the same fault by various investigators. It is important name or applying one of the original fault names to the that different names for the same fault not enter the Htera- entire length of the fault may be warranted. If such a change ture where future confusion is created. Here again, if the is proposed, the proposal should be accompanied by a de- State Geologist is regularly informed before publication, du- tailed analysis of the situation, well documented by maps, plicate fault names can be avoided and suitable arbitration fully explained in a text, and the proposal published in a can be provided in questions of priority of name, or of nam- recognized geological journal. A good example of this is the ing different traces of the same fault zone. case of the Espinosa, San Marcos, and Rinconada faults, now recognized as the same fault, for which Dibblee has A special problem arises when two or more separately proposed, in U.S. Geological Survey Professional Paper 981, mapped and named faults are found to join, after additional that the name Rinconada be applied to the entire length of work has been done. When this occurs, giving the fault a new the fault.

INDEX TO FAULT NAMES

Faults Usted are those shown on the 1975 edition of the Fault Map of California. To aid in their location, the 1° x 2° State Atlas

sheet on which the fault lies is indicated in parentheses. Abbreviations of sheet names are identified at the end of the list. An asterisk indicates a fault not shown, or not named, on the 1:250,000 scale Geologic Atlas.

Agua Cahente (SA) Claremont (SA, SB) •Grouse Point (W) Alamo Mt. thrust (LA) •Clark (SA) Halloran (K) Algodones (EC) Clearwater (LA) Harper (SB, T) Aliso (SA) •Coast Range thrust (LA, SR, Harris (SA) *Amedee (Su) R, W, U, SM, SJ, SC, SLO) Hayward (SF, SJ) Arroyo Parida (LA) Coast Ridge (SLO, SC) Healdsburg (SR) Bald Mountain (R, W) •Cold Fork (R) Helendale (SB) Banning (SA, SB) •Concord (SR, SJ, SF) •Hidalgo (SB) *Bat Mountain (DV) Coyote Creek (SA) Hidden Springs (SS) Bear Mountain (Sac, SJ) Coyote Lake (T) Hildreth (LA) Bear Valley (SC) Cristianitos (SA) Hilton (M) Ben Lomond (SF) Cucamonga (SB) Hitchbrook (LA) •Big Bend (C) •Cypress Point (SC) Hoadley (R) Big Pine (LA) •Dead Mountains (K, N) Holser (LA) Big Spring (SLO, B) Death Valley (see Northern •Honey Lake (Su, C) Blackwater (T) Death Valley-) •Hosgri (SLO, SM) Blake Ranch (SB) Death Valley Graben (DV) Hot Springs (C, SA-2, SS) Bloomfield (SR) •Death Valley, South (DV, T) Huasna, East (SLO) Blue Cut (SS, SA) •Del Norte (W) Imperial (EC) Blue Rock (SC) Dillon (SA, SB) Independence (F) •Bradley Canyon (SM) •Dogwood Peak (C) Ivanpah (K) •Brawley (EC, SS) Durrwood (B) Jawbone (B) Breckenridge (B) Earthquake Valley (SA) Jewett (B) •Browns Valley (SC) •East Fork (W, R) Johnson Valley (SB) Buena Vista (B) Edison (B) Jolon (SLO) Bullion (SB, N) Elder Creek (R) Kern Canyon (B, F) •Burdcll Mountain (SR) •El Modeno (SA) •Kern Front (B) Butano (SJ, SF) El Paso (T) •Kern Gorge (B) Cady (SB) Elsinore (SA, SD) •King City (SC) Calaveras (SC, SJ) Emerson (SB) Korbel (R) Calico (SB) Falor (R) •Laguna Salada (EC) Calico, West (SB) •Fort Sage (Su) •La Honda (SF) •Calipatria (EC, SS) Franklin (SF, SR) •La Nacion (SD) •Camel Peak (C) Freshwater (R) •La Panza (SLO, B) Camp Rock (SB) Furnace Creek (DV) Last Chance (C) Cantil Valley (T) Garhc Spring (T) Lenwood (SB) •Carmel Canyon (SC) Garlock (B, LA, T) Leuhman (SB) Casa Loma (SA) Garlock, North Branch (LA) Liebre (LA) Cedar Canyon (K) Garlock, South Branch (LA) Likely (A, Su) Chabot, East (SF) •Goat Ranch (B) •Litchfield (Su) Chamock (LA, LB) Green Valley (SR) Little Pine (LA, SM) Chino (SA, SB) Grizzly Valley (C) Little Salmon (R) Church Creek (SC) Grogan (W, R) Livermore (SJ) 1985 TEXT TO ACCOMPANY THE FAULT AND GEOLOGIC MAPS OF CALIFORNIA 79

Lockhart (T. SB) Panamint Valley (T, DV) Santa Rosa Island (SM) •Lockhart, South (T) Paskenta (U, R) Santa Susana thrust (LA) *Los Lobos (SC, SLO) Pastoria (LA) Santa Ynez (LA, SM) Los Pinos (SA) Pilarcitos (SF) Santa Ynez, South Branch (SM) •Lucia (SC) Pine Mountain (LA) Sargent (SC, SJ) Ludlow (SB, N) Pinnacles (SC) Sawpit Canyon (SB, LA) Madrone Springs (SJ) Pinto Mountain (SB, N) Seal Cove (SF) Malibu Coast (LA) Pinyon Peak (B) •Shady Canyon (SA) Mallethead thrust (W) Pipes Canyon (SB) •Sheephead (T) Manix (SB) Pisgah (SB) Sierra Madre (LA, SB) •Manly Pass (T) Pleasanton (SJ) Sierra Nevada (M, F, DV, T, B) •McCuUough (K) Pleito (LA, B) Silver Creek (SJ, SF) Melones (C, SJ, Sac, Su, M) •Point Reyes (SR, SF) •Simi (LA) •Mendocino (R) •Pond-Poso Creek (B) Spring (SB) Mesa (LA) Porcupine Wash (SS) •Spring Creek thrust (R) •Mesquite Lake (SB, N) Punchbowl (SB) Springs (B, LA) Midland (Sac, SJ) Raymond (Raymond Hill) (LA) •Stanford (SF) Mirage Valley (SB) Recruit Pass (B) State Line (K) Mission Creek (SB, SA) •Red Hill (SB) Stockton (Sac, SJ) •Mohawk Valley (C) Red Mountain (LA) Suey (SM) •Monterey Bay (SC) Refugio (SM) •Sulphur Spring (R) •Monterey Canyon (SC) Reliz (SC) Superstition Hills (SS, EC) Morales (B, LA) •Rialto-Colton (SB) Superstition Mountain (EC) More Ranch (LA) •Rich Bar (Su, C) Sur (SC) Morongo Valley (SB) Rinconada (SC, SLO, LA, SM) Sur-Nacimiento (SC) Mount Poso (B) Rodgers Creek (SR) Surprise Valley (A) Munson Creek (LA) Rosamond (LA) Sweitzer (SR) Muroc (T, B) •Rose Canyon (SD, SA) Tejon Canyon (B) Nacimiento (SLO) Salton Creek (SS) •Temescal (SA)

Newport-Inglewood (LB, LA, SA) San Andreas ( SS,SB, SA, LA. B, Tesla (SJ) Northern Death Valley-Furnace Creek SLO, SC, SJ, SF, SR, U, R) Tolay (SR) (M, DV) San Andreas, North Branch (SB) Tularcitos (SC) •North Fork (R, W) San Andreas, South Branch (SB) Tule Creek (LA) Northridge Hills (LA) San Benito (SC) •Twin Sisters (R, W) Norwalk (LB, SA) San Bruno (SF) Verdugo (LA) •Oak Flat (R) San Cayetano (LA) Vergales (SC) Oakridge (LA) •San Clemente (LB) Verona (SJ) Old Woman Springs (SB) •Sand Hills (EC, SS) Vincent thrust (SB) •Orleans (W) San Fehpe (SA) Walnut Creek (SB) Ortigalita (SJ, SC) San Fehpe Hills (SA) •Waltham Canyon (SC, SLO) •Owens VaUey (M, F, DV) San Francisquito (SC, LA) •White Mountains (M) Owl Lake (T) San Gabriel (LA, SB) Whiterock (B, LA) Ozena (LA) San Gregorio (SF) White Wolf (B) Pacifico (SM) San Jacinto (SA, SB) Whittier (SA, LB) Paicines (SC) San Jose (LA, SB, SJ, SF) Willow Creek (SC) •Palo Alto (SF) San Juan (SLO, B) •Willows (U, C) Palo Colorado (SC) Santa Cruz Island (LA, LB, SM) •Wilson Canyon (T) Palo Colorado-San Gregorio (SF, SC) •Santa Maria (SM) Yager (R) Palos Verdes (LB) Santa Monica (LA) Zayante (SF, SJ)

Abbreviations of Mop Sheets

A = Alturas M = Mariposa SLO = San Luis Obispo B = Bakersfield N = Needles SM = Santa Maria C = Chico R = Redding SR = Santa Rosa DV = Death Valley SA = Santa Ana SS = Salton Sea EC = El Centre Sac = Sacramento Su = Susanville F = Fresno SB = San Bernardino T = Trona K = Kingman SC = Santa Cruz U = Ukiah LA = Los Angeles SD = San Diego W = Weed LB = Long Beach SF = San Francisco WL = Walker Lake SJ = San Jose 80 DIVISION OF MINES AND GEOLOGY BULL. 201

SUPPLEMENTAL INDEX TO FAULT NAMES

Faults listed here are not shown on the 1975 edition of the Fault Map of California because of space problems, but they are shown on the individual sheets of the 1:250,000 scale Geologic Atlas of California, O. P. Jenkins edition. The sheets on which the faults occur are indicated in parentheses; abbreviations used are the same as those used in the previous index to faults.

Acton (LA) Glen Ivy (SA) Patterson Pass (SJ) Agua Blanca thrust (LA) Goose Lake (A) Pelican Hill (SA) Agua Dulce Canyon (LA) Gravel Pit (SJ) Pelona (LA) Agua Tibia (SA) Green Ranch (LA) Pick Creek (SC) Aguanga (SA) Greenville (SJ) Pine Rock (SC) Aliso Canyon (SA) Handorf (SB) Pinecate (SC) Amargosa thrust (T) Harper Lake (SB) Pinole (SF) Americano Creek (SR) Hillside (SF) Pinyon Hill (LA) Arnold Ranch (SA) Holmes (SB) Pole Canyon (LA) Arrastre Spring (T) Honda (SM) Protrero (LB) Ash Hill (DV) Huer Huero (SLO) (now La Panza) Red Hills (SLO) Avalon-Compton (LB) Indian Hill (SB) Rincon (SJ) Bee Canyon (LA) Indio Hills (SA) Round Mountain (B) Ben Trovato (SJ) Juncal Camp (LA) Russ (R) Berrocal (SJ) Keene Wonder (DV) San Antonio (SLO) Bicycle Lake (T) Kennedy (SR) San Dimas Canyon (SB) Black Butte (SJ) Kern River (B) (now Kern Gorge) San Guillermo (LA) Black Mountain (SR) Kramer Hills (SB) San Juan (SA) Bolinger (SF) Laguna Canyon (SA) San Marcos (SLO) Brown Mountain (T) Lancaster (SA) San Pablo (SF, SR) Bryant (SA) Las Tablas (SLO) Santa Rosa (LA) (now Simi) Buck Ridge (SA) Las Trampas (SF) Santa Ynez, North Branch (SM) Butte Valley (T) Lavigia (LA) Seal Beach (LB) Cabrillo (LB) Lawrence (SA) Shannon (SJ) Cajon Valley (SB) Leach Lake (T) Sidewinder (SB) Cameros (LA) Limekiln (SJ) Sierra Azul (SJ) Camuesa (LA) Little Oak Canyon (LA) Soda Creek (SR) Carnegie (SJ) Little Rock (LA) Soda Spring (SJ) Cameros (SR) Little Sulphur (SR) Soledad (LA) Chabot (SF) Lockwood (LA) South (K) Chalone Creek (SC) Loma Aha (LA) South Fork Mountain (R, W) Cherry Hill (LB) Loma Linda (SB) Southhampton (SR) Childers Peak (SR) Lone Tree (LA) St. John Mountain (SR) Chimeneas (SLO) Maacama (SR) Stewart (SA) Clark Mountain (K) Magic Mountain (LA) Stony Brook (SJ) Cleghom (SB) Maguire Peaks (SJ) Stony Creek (U) Clemens Well (SS) Mattole (R) Sunol (SF) Collayomi (SR) McWay thrust (SC) Sycamore (LA) Cook Peak (B) Mecca Hills (SA) Temple Hill (SA) Cottonwood (LA) Mesquite (SB) (now Mesquite L.) Tenaja (SA) Cox Ranch (SA) Mesquite thrust (K) Thomas Mountain (SA) Cull Creek (SF) Middle (K) Towne (DV) Curry Mountain (SC) Midway (SJ) Tracy (Stockton) (SJ) Cuyama (SLO) Mill Creek (SB) Transmission Line (LA) Cuyama, South (LA) Miller Creek (SF, SC) Tyler Horse (LA) Diamond Bar (SA) Mint Canyon (LA) Tyler Valley (SB) Doble (SB) Mission (SJ) Valle (SJ) Dos Pueblos (LA) Mission Ridge (LA) Vasquez Canyon (LA) Dry Creek (LA) Mount Diablo (SJ) Water Tank (SJ) Duarte (SB) Mount Jackson (SR) Welch (SJ) Dublin (SJ) Mule Spring (T) West Huasna (SLO) Eisner (SR) Nadeau (LA) Wildcat (SF) Espinoza (SC, SLO) New Idria thrust (SC) Wildomar (SA) False Cape Shear Zone (R) North (K) Wilhams (SJ) Fitch Mountain (SR) North Fork (SC) Willow Springs (LA) Frazier Mountain, North (LA) Old Dad (K) Wilson (SR) Frazier Mountain, South (LA) Orocopia thrust (SS) Winters thrust (K) Gandy Ranch (SA) Overland Avenue (LA) Woods (SR) Garnet Hill (SA) Palm Canyon (SA) Workman Hill fault extension (LA) Glen Anne (LA) Park Hill (SA) Wragg Canyon (SR) Glen Helen (SB) Parks (SJ) 1985 TEXT TO ACCOMPANY THE FAULT AND GEOLOGIC MAPS OF CALIFORNIA 81

APPENDIX B

TABULATED LIST OF THERMAL SPRINGS AND THERMAL WELLS

The following tabulation provides additional data for the ther- and wells were made. If later reports did not clarify the locations, mal springs and wells shown on the Fault Map of California. county records were examined (old copies of official county These data include information on location, water temperature, maps, as well as early Mines and Mineral Resources Reports by references, notes, in wells, some and, the case of the total depth the California Division of Mines and its predecessor, the State and year drilled. Mining Bureau). Particularly useful in locating many early ther- mal springs and resorts was a book entitled "Mineral Springs DATA USED AND and Health Resorts of California" (1892), by Winslow Ander- son, Professor of Medicine at the University of California Medi- ACKNOWLEDGMENTS cal School, San Francisco. Because the early references often did not give the location of the thermal springs and wells by town- ship, range, and section, these data were often Multiple references are often indicated on the tabulated Ust determined by the compilers where possible, from 7'/;- or because in many instances supplementary references can be help- 15-minute quadrangles. In unsurveyed land, the locations were described by the compilers ful in locating the spring or well more precisely on a map or in by latitude and longitude from the published quadrangles. finding it in the field. In addition, many of these references The thermal springs and wells are shown on the Source (especially the more recent ones) contain data pertaining to Data Index maps (Appendix D) as circles for theimal springs chemistry and physical properties (for example, conductivity, and as squares for thermal wells. These spring and well locations discharge rate, and isotopic analysis). In addition to the pub- are numbered, starting with "1" (one) for each atlas Ushed references Usted, unpubUshed data were acquired from sheet. These coded numbers refer to the tabulated data in the following Robert W. Rex (Repubhc Geothermal, Inc.), James B. Koenig Ap- pendix B. On the Fault Map of CaUfomia, the thermal springs (Geothermex), and Sanford L. Werner (California Department and wells are shown, but are not coded by number. of Water Resources). To these, I wish to express my gratitude. It should be noted that a number of the thermal springs Help in plotting and tabulating these data was ably provided by are actually shallow wells that were dug or drilled for water John Sackett, Melvin C. Stinson, Robert A. Switzer, and Duane but came in flowing A. McClure. as artesian wells. Oftentimes such artesian wells were dug for convenience in areas where no springs occur, so both wells and springs are intimately associated and, in fact, on the early records often the two are not clearly differentiated. LOCATING THERMAL SPRINGS Following the convention estabhshed in reports by G. A. War- ing (1915 and 1965), which were the principal sources used AND WELLS when this present compilation was started, the writer considered as thermal only those springs that are more than 15°F (8.3°C) above the mean annual temperature of the air at their locaUties. Locations of many thermal springs and wells, especially many In the case of drilled wells, a normal thermal gradient of about of those listed in the earher publications, were vague and difficult IT increase for each 100 feet of depth (2°C for each 100 meters) to plot. A reason for this was the lack of adequate base maps for was taken into consideration when determining whether the well many parts of the state when these earUer reports on hot springs should be classified as thermal. 82

ALTURAS SHEET 1985

SHEET 1 TURAS 84 DIVISION OF MINES AND GEOLOGY BULL. 201

ALTURAS SHEET APPENDIX B - TABULATED LIST OF THERMAL SPRINGS AND WELLS KW• LOC. NO. 1985 TEXT TO ACCOMPANY THE FAULT AND GEOLOGIC MAPS OF CALIFORNIA 85

ALTURAS SHEET APPENDIX B - TABULATED LIST OF THERMAL SPRINGS AND WELLS 86 DIVISION OF MINES AND GEOLOGY BULL. 201

CHICO SHEET APPENDIX B - TABULATED LIST OF THERMAL SPRINGS AND WELLS

7\ MAP LOC. NO. 1985 TEXT TO ACCOMPANY THE FAULT AND GEOLOGIC MAPS OF CALIFORNIA 87

DEATH VALLEY SHEET APPENDIX B - TABULATED LIST OF THERMAL SPRINGS AND WELLS

HAP LOC. HO. 88 DIVISION OF MINES AND GEOLOGY BULL. 201

EL CENTRO SHEET APPENDIX B - TABULATED LIST OF THERMAL SPRINGS AND WELLS

• MAP LOC. NO. 1985 TEXT TO ACCOMPANY THE FAULT AND GEOLOGIC MAPS OF CALIFORNIA 89

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HAP LOC. NO. 90 DIVISION OF MINES AND GEOLOGY BULL. 201

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EL CENTRO SHEET APPENDIX B - TABULATED LIST OF THERMAL SPRINGS AND WELLS

• HAP UX. SO. 92 DIVISION OF MINES AND GEOLOGY BULL. 201

LOS ANGELES SHEET APPENDIX B - TABULATED LIST OF THERMAL SPRINGS AND WELLS • HAP UK. NO. 1985 TEXT TO ACCOMPANY THE FAULT AND GEOLOGIC MAPS OF CALIFORNIA 93

LOS ANGELES SHEET APPENDIX B - TABULATED LIST OF THERMAL SPRINGS AND WELLS

• HAF LOC. NO. 94 DIVISION OF MINES AND GEOLOGY BULL. 201

MARIPOSA SHEET APPENDIX B - TABULATED LIST OF THERMAL SPRINGS AND WELLS

LOC. NO. 1985 TEXT TO ACCOMPANY THE FAULT AND GEOLOGIC MAPS OF CALIFORNIA 95

MARIPOSA SHEET APPENDIX B - TABULATED LIST OF THERMAL SPRINGS AND WELLS

map" LOC. NO. 96 DIVISION OF MINES AND GEOLOGY BULL. 201

SALTON SEA SHEET APPENDIX B - TABULATED LIST OF THERMAL SPRINGS AND WELLS

• HAP LOC. NO. 1985 TEXT TO ACCOMPANY THE FAULT AND GEOLOGIC MAPS OF CALIFORNIA 97

SALTON SEA SHEET APPENDIX B - TABULATED LIST OF THERMAL SPRINGS AND WELLS

MAP LOC. SO. 98 DIVISION OF MINES AND GEOLOGY BULL. 201

SALTON SE* SHEET APPENDIX B - TABULATED LIST OF THERMAL SPRINGS AND WELLS

LOC. HO. 1985 TEXT TO ACCOMPANY THE FAULT AND GEOLOGIC MAPS OF CALIFORNIA 99

SALTON SEA SHEET APPENDIX B - TABULATED LIST OF THERMAL SPRINGS AND WELLS

UX. NO. 100 DIVISION OF MINES AND GEOLOGY BULL. 201

SAN BERNARDINO SHEET APPENDIX B - TABULATED LIST OF THERMAL SPRINGS AND WELLS

• NAP UX. KO. 1985 TEXT TO ACCOMPANY THE FAULT AND GEOLOGIC MAPS OF CALIFORNIA 101

SAN DIEGO SHEET APPENDIX B - TABULATED LIST OF THERMAL SPRINGS AND WELLS

MAT LOC. NO. 102 DIVISION OF MINES AND GEOLOGY BULL. 201

SAN JOSE SHEET APPENDIX B - TABULATED LIST OF THERMAL SPRINGS AND WELLS • NAP UX. NO. 1985 TEXT TO ACCOMPANY THE FAULT AND GEOLOGIC MAPS OF CALIFORNIA 103

SANTA ANA SHEET APPENDIX B - TABULATED LIST OF THERMAL SPRINGS AND WELLS

• MM' LOC, HO. 104 DIVISION OF MINES AND GEOLOGY BULL. 201

SANTA ANA SHEET APPENDIX B - TABULATED LIST OF THERMAL SPRINGS AND WELLS

LOC. NO. 1985 TEXT TO ACCOMPANY THE FAULT AND GEOLOGIC MAPS OF CALIFORNIA 105

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LOC. HO. 1985 TEXT TO ACCOMPANY THE FAULT AND GEOLOGIC MAPS OF CALIFORNIA 107

SANTA ANA SHEET APPENDIX B - TABULATED LIST OF THERMAL SPRINGS AND WELLS • KAF UX. NO. 108 DIVISION OF MINES AND GEOLOGY BULL. 201

SANTA CRUZ SHEET APPENDIX B - TABULATED LIST OF THERMAL SPRINGS AND WELLS

HkF UK. NO. 1985 TEXT TO ACCOMPANY THE FAULT AND GEOLOGIC MAPS OF CALIFORNIA 109

SANTA ROSA SHEET APPENDIX B - TABULATED LIST OF THERMAL SPRINGS AND WELLS

uv. NO. no DIVISION OF MINES AND GEOLOGY BULL. 201

SANTA ROSA SHEET APPENDIX B - TABULATED LIST OF THERMAL SPRINGS AND WELLS

NAP* LOC. NO. 1

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vx- NO. 112 DIVISION OF MINES AND GEOLOGY BULL. 201

SUSANVILLE (wESTWOOD) SHEET APPENDIX B - TABULATED LIST OF THERMAL SPRINGS AND WELLS

• MAP UX. NO. 1985 TEXT TO ACCOMPANY THE FAULT AND GEOLOGIC MAPS OF CALIFORNIA 113 sus/ 114 DIVISION OF MINES AND GEOLOGY BULL. 201

TRONA SHEET APPENDIX B - TABULATED LIST OF THERMAL SPRINGS AND WELLS

HAP LOC. NO. 1985 TEXT TO ACCOMPANY THE FAULT AND GEOLOGIC MAPS OF CALIFORNIA 1 15

UKIAH SHEET APPENDIX B - TABULATED LIST OF THERMAL SPRINGS AND WELLS

• HAP LOC. NO. 116 DIVISION OF MINES AND GEOLOGY BULL. 201

WALKER LAKE SHEET APPENDIX B - TABULATED LIST OF THERMAL SPRINGS AND WELLS

• KM- LOC. NO. 1985 TEXT TO ACCOMPANY THE FAULT AND GEOLOGIC MAPS OF CALIFORNIA 117

WEED SHEET APPENDIX B - TABULATED LIST OF THERMAL SPRINGS AND WELLS

MAP UX". NO. 118 DIVISION OF MINES AND GEOLOGY BULL. 201

ABBREVIATION COMPLETE REFERENCE

CDWR Bull. 143-7 California Deportment Water Resources, 1970, Geothermcl wostes and the water resources of the Salton Sea area: Bulletin

No. 143-7, 123 p.

CDWR Long Valley Invest. California Department Water Resources, 1967, Investigation of geothermol v»aters in the Long Valley area, Mono County, 141 p.

CDWR Mom. Bosin Rept. California Department Water Resources, 1973, Mammoth basin woter resources environmentol study. Final Report, 70 p.

CDWR-UCR Dunes Rept. Coplen, T.B., and others, 1973, Preliminary findings of on investigation of the Dunes thermal onomoly. Imperial Valley,

California: California Department of Water Resources ond University of California, Riverside, 48 p.

OMG V. 41, no. 3 Tucker, W.B., and Sampson, R.J., 1945, Mineral Resources of Riverside County: California Division of Mines, California Journal of Mines and Geology, v. 41, no. 3, (p. 178, Highland Springs).

Comegie Inst. Wosh. Pub. 360 Day, A.L., and Allen, E.T., 1925, The volcanic activity and hot springs of Lassen Peak: The Carnegie Institute of Washington,

Publication 360, 190 p.

Koenig, 1968 Koenig, J.B., 1968, Field trip guide to The Geysers, Sonoma County, California: Northern California Geological Society Field Trip Guide.

Rex, unpub. Rex, R.W. (Republic Geothermmol, Inc., Whittier, CA) , Computer print-out list of data on geothermol wells in Imperial and Coachello Valleys, 1972.

uses GO 437 Huber, N.K., and Rinehort, CD., 1965, Geologic map of the Devils Postpile quadrangle. Sierra Nevoda, California: U.S. Geological Survey Geologic Quadrangle Map GQ-437.

USGS Geoth. Modoc Co. [open Duffield, W.A., and Fournier, R.O., 1974, Reconniossonce study of the geothermol resources of Modoc County, California,

file) U.S. Geological Survey Open-File Report, 19 p.

USGS MF 577 Clark, J.C, and others, 1974, Preliminary geologic map of the Monterey and Seaside 7V2' quadrangles, Monterey County, California with emphasis on active faults; U.S. Geological Survey Miscellaneous Field Studies Map MF 577.

USGS Open File (Imperial Vo.) Hordt, W.F., and French, J. J., 1976, Selected data on water wells, geothermol wells, and oil tests in Imperial Valley, California: U.S. Geological Survey Open-File Report, 251 p.

USGS PP 385 Rinehort, CD., and Ross, D.C, 1964, Geology and mineral deposits of the Mount Morrison quadrangle, Sierra Nevada,

California: U.S. Geological Survey Professional Paper 385, 106 p.

USGS PP 440-F White, D.E., Hem, J.D., ond Waring, G.A., 1963, Chemical composition of subsurfoce waters. Chapter F, in Doto of

geochemistry: U.S. Geological Survey Professional Paper 440-F, 67 p.

USGS PP 457 Smith, G.I., 1964, Geology and volcanic petrology of the Lovo Mountoins, Son Bernardino County, California: U.S.

Geological Survey Professional Paper 457, 97 p.

USGS PP 486-G Metzger, D.G., Loeltz, O.J., and Irelan, B., 1973, Geohydrology of the Porker-Blythe-Cibolo area, Arizona and California:

U.S. Geological Survey Professional Paper 486-G, 130 p.

USGS PP 492 Waring, G.A., 1965, Thermal springs of the United States and other countries of the world—A summary: U.S. Geological Survey Professional Paper 492, 383 p.

USGS Woter Res. Div. Open File Berkstresser, C.F., Jr, 1969, Data for springs in the Colorado Desert area of California: U.S. Geological Survey Open-File (Colo. Desert) Report, 13 p.

USGS Water Res. Div. Open File Berkstresser, C.F., Jr., 1968, Data for springs in the northern Coast Ranges and Klamath Mountains of California: U. S.

(No. Coast & Klamath Mtns.) Geological Survey Open-File Report, 49 p.

USGS Water Res. Div. Open File Berkstresser, C.F., Jr., 1968, Data for springs in the southern Coast, Transverse, ond Peninsular Ronges of California;

(So. Coast - Penin. Ranges) U.S. Geological Survey Open-File Report, 21 p.

USGS WRI 13-73 Foye, RE., 1973, Ground-woter hydrology of northern Napa Valley, California: U.S. Geological Survey Water-Resources

Investigations, 13-73, 64 p.

USGS WRI 33-73 Moyle, W.R., Jr., 1974, Temperature and chemical data for selected thermal wells and springs in southeastern California;

U.S. Geological Survey Water-Resources Investigations 33-73, 12 p.

USGS WSP 142 Mendenhall, W.C, 1905, The hydrology of Son Bernardino Valley, California: U.S. Geological Survey Woter-Supply and

Irrigation Paper No. 142, 124 p.

USGS WSP 338 Waring, G.A., 1915, Springs of Colifornio: U.S. Geologicol Survey Woter-Supply Paper 338, 410 p.

USGS WSP 1548 Cordwell, G.T., 1965, Geology ond ground water in Russian River Valley areas ond in Round, Loytonville, and Little Lake

Valleys, Sonoma and Mendocino counties, California: U.S. Geologicol Survey Water-Supply Paper 1548, 154 p.

Werner, unpub. Werner, S.L. (California Department Woter Resources), List of data on geothermol wells in Imperial Valley (from talk, 1974).

Zeitschrift fiir Vulkonologie Willioms, Howel, 1934, Mount Shasta, California; Zeitschrift fur Vulkonologie, vol. 15, pp. 225-253. 1985 TEXT TO ACCOMPANY THE FAULT AND GEOLOGIC MAPS OF CALIFORNIA 119

APPENDIX C

INDEX TO THE GEOLOGIC FORMATIONS GROUPED WITHIN EACH UNIT PORTRAYED ON THE GEOLOGIC MAP OF CALIFORNIA, 1977 EDITION

Obviously, all the individual formations mapped in California, Many formations in the following list are described in paren- of which there are well over 1,000, could not be depicted on the theses as "(in part)." This was done where a formation is com- lithologies dissimilar origin. 1 :750,000 scale Geologic Map of California. As explained in Part pKjsed of rocks of vastly different or II of this bulletin, the units portrayed on the Geologic Map are For example, a sedimentary formational unit may have volcanic drawn on the basis of formation boundaries, but there are nu- members within it. In such a case, the volcanic members would merous formations contained within many of the mapped units. be grouped with the volcanic units (of comparable age as the These formations are not portrayed on the map or named in the sedimentary unit). Likewise, a marine formational unit may geologic legend—only a description of the predominant litholog- have interbedded nonmarine members, and these would in most ic types for each mapped unit is given there. For a complete and cases (if extensive enough to show) be grouped with the nonma- detailed listing of the individual formational units in California, rine map unit of appropriate age. along with cross indexes by geologic age and by map sheet areas, Most of the designated units on the 1977 map contain the the reader is referred to the "Geologic Legend and Formation formational units depicted on the State Geologic Atlas sheets; Indexes" which accompany the Geologic Atlas of California. however, where subsequent work has shown that certain forma- The index of geologic formations presented in the following tions were of a significantly different age than what was previ- pages is much more generalized than that of the Atlas; it was ously considered (probably as a result of the discovery of new designed not to supplant the Atlas index, but rather to provide or more-diagnostic fossils, or by reason of more accurate strati- an easy-to-use listing that is referenced directly to the units graphic correlations), the results of this new information were portrayed on the 1:750,000 Geologic Map of California. taken into consideration, and the formation was depicted in the most appropriate way on the new State Geologic Map. Several new geologic units are shown on the 1977 map that EXPLANATION were not recognized on the State Geologic Atlas. These include several areas in the southeastern part of the state where Tertiary

In preparation of the 1 :75O,0OO scale Geologic Map of Califor- granitic rocks have been dated (gr*^ ); an extensive belt of Terti- nia, the mapped formations in the state were grouped into 52 ary-Cretaceous rocks in the northern Coast Ranges, known as units according to lithologic similarities and rock origins, and the Coastal Belt rocks or "Coastal Belt Franciscan" (TK); two were also arranged chronologically, according to relative age. locations of newly recognized Paleozoic (or Permo-Triassic)

The contacts for the units shown on the 1977 map are therefore granitic rocks (gr*^) , one location in northern California and one based on actual formation contacts—if not individual formations in the southern part of the state; and two subdivisions within the —then grouped formations. The following list shows what for- Franciscan Complex—a melange unit (KJf„) and a schist unit mations were grouped into each map unit shown by the different (KJf.). symbols on the 1:750,000 scale map. This, of course, is a state- If the reader would like a more detailed description of the wide synthesis, and in any one location either a single formation individual formational units listed in the following table, he may

is represented or two or more formations have been grouped. refer to the various stratigraphic nomenclature sheets that ac- Because geologic formations commonly transcend time bounda- company the individual Geologic Atlas sheets or to the source ries, many formations listed on the following table do not strictly data from which the Geologic Atlas was derived, as indicated on

fit the time interval indicated. It was not only more practical but the explanatory data accompanying each sheet. also more meaningful in compiling the map to conform to forma- For a more detailed explanation of the way in which the rock tion boundaries, which can be more easily related to the rocks units were classified, and for a discussion of special stratigraphic in the field, than to try and "take apart" the geologist's forma- problems encountered in preparing the 1:750,000 State Geologic tion and draw "time" lines. Map, one should refer to pages 58- 63 in Section II. 120 DIVISION OF MINES AND GEOLOGY BULL. 201

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APPENDIX D

SOURCE DATA INDEX

Following the format of earlier Division of Mines and Geol- OTHER REFERENCES I ogy indexes to published geologic maps and indexes to theses (see below), this index is organized by State Geologic Atlas sheets (generally 1° x 2° quadrangles). In determining the refer- For more extensive references to areal geologic mapping, the ences used for any particular area on the Geologic Map of Cali- reader is referred to the following publications of the California fornia, or the basis on which a fault was classified on the Fault Division of Mines and Geology: Map of California, the map-user must first determine the State Atlas sheet on which his area of interest lies. If not particularly familiar with these sheets, the map-user should refer to the State Indexes to Published Geologic Maps Index Map (Figure 16), which shows the boundaries of the individual Atlas sheets. Once the map-user knows the appropri- Special Report 52, Index to Geologic Maps of California to ate Atlas sheet, he can use the index map and bibliography for December 31, 1956, by R. G. Strand, J. B. Koenig, and C. W. that sheet to determine the source data used. Jennings.

Special Report 52-A, Index to Geologic Maps of California, HOW TO USE THIS INDEX 1957-1960, by J. B. Koenig. Special Report 52-B, Index to Geologic Maps of California, This index should be used in conjunction with the "Index to 1961-1964, by J. B. Koenig and E. W. Kiessling. Geologic Mapping" accompanying each sheet of the Geologic Atlas of California, 1:250,000 series. It supplements the source Special Report 102, Index to Geologic Maps of CaUfomia, 1965- data given in the Atlas sheet indexes; only references that were 1968, by E. W. Kiessling. published or acquired subsequent to the issuance of the corre- sponding State Geologic Atlas sheet, as well as additional refer- Special Report 130, Index to Geologic Maps of California, 1969- ences that were used in classifying faults, are shown in Appendix 1975, by E. W. Kiessling and D. H. Peterson. D. Some of these references were received late, and may not have been used (or were used only in part) in the compilation of the Fault Map of California and the Geologic Map of California. Indexes to Theses They are included here because of their potential usefulness to persons seeking more recent references for an area. * Because the primary purpose of the Fault Map of California Special Report 74, Index to Graduate Theses on California Geol- is to provide more information on individual faults, especially for ogy to December 31, 1961, by C. W. Jennings and R. G. active or potentially active ones, particular attention has been Strand. given to providing references to the historic and Quaternary faults. For ease in locating references on specific historic or Special Report 115, Index to Graduate Theses and Dissertations Quaternary faults, the index maps have selectively shown these on California Geology, 1962 through 1972, by G.C. Taylor. faults, albeit in a generalized and simplified form (using solid and dotted lines only). For more accurate depiction of these California Geology, February 1978, Index to Graduate Theses faults, the reader should refer to the 1:750,000 Fault Map of and Dissertations on California Geology, 1973 and 1974, by California. If no source data are given for a specific fault shown D.H. Peterson and G.J. Saucedo. on the index sheets, then the reference (s) used were taken from the published 1:250,000 State Geologic Atlas sheets, and the California Geology, April 1978, Index to Graduate Theses and reader should consult the Atlas and its accompanying source Dissertations on California Geology, 1975 and 1976, by D. H. data indexes. Peterson and G. J. Saucedo.

•Becaust of the lale publication of this Bulletin (more than ten years after the compilation of the Fault Map of California and the Geologic Map of California), many of the references cited in Appendix D as "work in progress" have subsequently been published Because of subsequent changes that may have occurred from the "work in progress" stage to the final published work, no attempt has been made to update this Source Data Index with later references. Hence the references cited in Appendix D are largely those that were actually used in the compilation of the Fault and Geologic Maps The source data should be quite complete to approximately 1972 In a few- instances this Source Data Index contains some references up to 1975 that were added after the Stale maps had been compiled and while the text of this bulletin was being wntten 126 DIVISION OF MINES AND GEOLOGY BULL. 201

Figure 16. Slote index mop showing the boundories of the individuol Geologic Alias sheets ond the source doto index mops in Appendix D. 1985 TEXT TO ACCOMPANY THE FAULT AND GEOLOGIC MAPS OF CALIFORNIA 127

EXPLANATION OF MAPS

On the following index maps of Appendix D, some of the boundary lines are solid and some are dashed. The dashed boundaries indicate one of the following:

(a) The extent to which a source map was used—that is, that the source map continues farther, but that other data were used beyond the dashed boundary.

(b) The area enclosed includes only selected data, for exam- ple, fault data only.

(c) The boundary of one map, where two or more maps overlap—in the interest of clarity in cases of overlapping source data. 128 DIVISION OF MINES AND GEOLOGY BULL. 201

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STATE OF CALIFORNIA- GEC THE RESOURCES AGENCY - GORDON K. DEPARTMENT OF CONSERVATIO!

>v STATE OF CALIFORN DIVISION OF MINES AND GEOLOGY THE RESOURCES AGENCY - G( JAMES F DAVIS. STATE GEOLOGIST DEPARTMENT OF CON!

A Structural Piofincei MAP of Colilornlo daletmined by the prominent foult paltemt and ehorocteri»fi« of Hn faulti they tonioin or bound. lEncitcled numberi in lower port of mop identify certain foulti referred to in te»t.) RGE DEUKMEJIAN, GOVERNOR 'AN VLECK, SECRETARY FOR RESOURCES Faull ond Geologic Data Mops of California I BLUBAUGH, DIRECTOR -DON L BULLETIN 201. PLATE 2

MAP B; Parollelilm Quoternory between major faults and regularity of foolt spacing. ( Encirc^d numbers lower in portion of mop identify certoin faults referred to in the text.) MAP C: Relotionship of eorthquoke epicerXers to foulls in Colifornia, Note the close relationship of eorthquokes of magnitude 6 ond greoter to the mojor Quoternory foults. (Epicenters from Eorthquoke Epicenter Mop Of Colifornio, 1900-1974, by C.R. Real, T.R. Toppozodo ond O.L. Pofke, 1978-1

OD n MAP Dl Earthquake epicenters of magnitude 4 to 4.9 showing more scatter than for the lorger earth- quakes, but olio suggesting certain oreos of low historic seismicity. (Epicenters from Earthquake Epicenter Mop Of Colifornio, 19001974, by C.R. Real. T,R, Toppoiobo, ond DL. Porke. 1978.)

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