San Andreas : History of concepts

MASON L. HILL 1401,7 E. Summit Drive, Wbitticr, 90602

ABSTRACT strike-slip on the San Andreas (Noble, 1926); (3) the proposal of more than 560 km of cumulative right-slip on the fault (Hill and The long and active was revealed by the San Dibblee, 1953); and (4) the introduction of the San Andreas as a Francisco of 1906. Strike-slip movement on a major separating major crustal plates (Wilson, 1965). crustal fracture was first established by that event. The elastic re- Justification for this history is to show how concepts about the San bound theory was developed in an analysis of this earthquake. It Andreas fault have changed, and to indicate that future studies will was proposed in 1926 that cumulative horizontal movement on the result in new interpretations. My authorship may be justified by San Andreas amounted to several miles, but such a great displace- knowing some of the and many of the geologists involved ment was generally agreed to be unreasonable. In 1953, new evi- in this history. History writing, like much in science, is in large dence of cross-fault stratigraphic correlations of Pleistocene to Cre- measure subjective. Thus, it will be obvious to the reader that I taceous rocks was presented which seemed to require tens to hun- have "axes to grind." Specifically, I object to (1) confusion between dreds of miles of strike-slip displacement. Controversy and fault separation and fault slip; (2) the long-held assumption that additional studies ensued, resulting in general acceptance of such Franciscan strata were deposited on granitic rocks; (3) resistance to movements by 1968. Since the 1965 proposal that the San Andreas miles of strike-slip on the fault; and (4) the present tendency to ac- is a transform fault, within a plate- mechanism, reser- cept a simplistic role for the San Andreas in . Em- vations about great horizontal movements of the Earth's crust have phasis is placed on the roles of new data and new insights in the been essentially eliminated. The single most important factor in de- evolution, or revolutions, in concepts about the San Andreas. Sev- laying acceptance of miles of strike-slip on the San Andreas has eral controversies are recorded to show how they have stimulated been the long-continued confusion between fault separation and new studies and new interpretations. However, the overriding fault slip. Lawson, Noble, Taliaferro, Hill and Dibblee, Wilson, incentives to intensified studies of the San Andreas have been (1) and a few others played the more leading roles in interpretations of the earthquake; (2) the proposals of tens to hundreds the fault. Post-earthquake studies by Gilbert again confirmed his of miles of cumulative strike-slip, (3) the recent interpretation of reputation as a great geologist. The San Francisco earthquake was the San Andreas as a transform fault; and (4) the currently inten- the chief contributor to knowledge about the San Andreas, but now sified research on earthquake prediction. there are more questions than ever regarding the , geologic This history of work on the San Andreas cites the studies and in- history, and significance of-this important crustal structure. The volvement of many persons of renown. Some of them are recog- present consensus about the role of the fault in local and global nized in brief biographic sketches, alphabetically arranged in Ap- tectonics surely will be modified by revolutionary new conceptual pendix 1, and identified by asterisks in the text. models. THROUGH THE 1906 EARTHQUAKE INTRODUCTION

It appears that Lawson" was the first to recognize, map, and This historical account of recognition, mapping, and interpreta- refer in print to a segment of the San Andreas fault. (Refer to Fig. 1 tions of the San Andreas fault provides background for present for location of San Andreas fault and a few of the places mentioned concepts and problems relating to this important structure. The San in the text. A good geographic-geologic reference for some readers Andreas is an important crustal fracture because it (1) is at least is the 1:750,000 Geologic Map of California by Jennings, 1977.) 960 km long; (2) produces great ; (3) is characterized His description, probably based on field work beginning in 1890 or by strike-slip displacement; (4) has a generally agreed upon 1 891, appeared in the first volume of University of California, Bul- cumulative right-slip of ~320 km; and (5) is widely accepted as a letin, Department of Geology, in "The post-Pliocene diastrophism transform fault which separates the North American and Pacific of the coast of " (Lawson, 1893). He said (p. lithospheric plates. 149): The history recounted here begins with the initial mapping of segments of the fault, follows with highlights of continuing studies The line of demarkation between the Pliocene and Mesozoic terraines is a and interpretations, and concludes with an analysis of this history nearly straight [northwest trending] line coincident with the projection of and its possible bearing on future studies of the San Andreas. The the axis of San Andreas Valley to Mussell Rock. selection of accounts considered to be significant, and their role in this history, are surely colored by personal bias and are, in some He also explained (p. 150) the uplift and presumed erosion down measure, self-serving. The story is separated into five eras by (1) the into Mesozoic rocks southwest of the fault by "orogenic upthrust" State Investigation Commission's report on the 1906 earthquake against the Pliocene Merced series to the northeast, with sub- (Lawson, 1908; Reid, 1910); (2) the suggestion of 38 km of sequent epeirogenic uplift of both the Pliocene and Mesozoic ter-

Geological Society of America Bulletin, Part 1, v. 92, p. 112-131, 1 fig., March 1981.

112

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ranes. His section (p. 146) indicates the position of the fault with- fault separation (geometry) and fault slip (kinematics) has been ac- out showing offset. Lawson did not name the fault or give it any commodated by a dual classification of faults (Hill, 1959). importance except in the context of the paper's title. Even after the Branner seems to have been the second geologist to have evidence of strike-slip at the time of the earthquake, Lawson and mapped a segment of the San Andreas fault, although according to others continued to infer that the offsets revealed in geologic sec- Jordan (1907), Branner was first. However, since Branner did not tions resulted from dip-slip movements. This confusion between come to Stanford until the fall of 1892, I doubt that his mapping preceded Lawson's. Lawson (1895) apparently first introduced the name, "San An- dreas fault," in the 15th Annual Report of the U.S. Geological Sur- OREGON vey. His 77-page account, Sketch of the Geology of the San Fran- cisco Peninsula, was professed to be (p. 406):

the first time the method of systematic mapping has been applied to the study of the Coast Ranges, and the results have strengthened the writer's conviction that this is the only effective method of arriving at clear concep- tions of their general geology.

His colored map clearly shows the San Andreas lineament extend- ing southeastward from through Lake San Andreas and Crystal Springs Lake. In describing the structure of the , Lawson discussed the fault-bounded San ^SHELTER COVE Bruno and Montara Mountains. Describing the geology within the Montara Mountain block, he wrote (p. 468):

The deformation of the Merced series [isj along a line of its present contact with the Franciscan terrane, i.e., along a line coincident with the San An- dreas fault. LPT. ARENA 9\ W 1906 BREAK AND EPICENTER

k PT. REYES \ \

kSAN\FRANCISCO PENINSULA \ ft \ i SAN JUAN BAUTISTA o o dì CHOLAME \ N 7.P Q, 1857 BREAK AND EPICENTER S \ \ FT TEJON ANSVERSE SAN GABRI MOUNTAINS RANGES GORGON IO PASS

100 200 300 400 km * *

Figure 1. Index map, San Andreas fault, California.

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This casual use of the name "San Andreas" for the fault is the only Osmont (1904) appears to have been the next geologist to map one in this report. Clearly it was not considered an important struc- and describe segments of the San Andreas fault before the 1906 ture. However, its name is appropriate and Lake San Andreas can earthquake. His two long geological traverses from the Pacific be accepted as the fault's "type locality." Ocean to the crossed the San Andreas in Marin It appears that the third geologist to describe, although not map, County, where it was called the Baulinas-Tomales fault. He refer- a segment of the San Andreas fault was Fairbanks5' (1894), who red to the fault (p. 79) as follows: said (p. 495): At Bodego Head (section AB) and Peninsula (section CD) the pre-Franciscan granitics (diorite) have probably been brought to light by a The effects produced by a great earthquake, probably that of 1872, can be great fault along the line of Bodega and Tómales Bay, seemingly the north- traced a number of miles along the stage road from Gorman Station to An- west extension of the San Bruno fault ... of the San Franciscan Peninsula. telope Valley, where large depressions still exist. Osmont obviously followed Anderson (1899) in inferring reversals This short sentence contains some errors: an earthquake did not of throw on this fault, and its connection with Lawson's (1895) San produce this line of ground depressions, nor did one fault dis- Bruno fault. He stated (p. 48), placement, and the 1857 , not the 1872 , earthquake was produced by movement on this fault zone. But we know that they [granitic rocks] lie unconformably below the Fran- Schuyler (1896) in his comprehensive paper entitled Reservoirs ciscan. . . . for Irrigation, in the 18th Annual Report of the U.S. Geological Survey, described a fault (the San Andreas) on the north side of the The last of the eight accounts of segments of the San Andreas Sierra Madre (San Gabriel) Mountains as follows (p. 711-712): fault that appeared before the San Francisco earthquake seems to be the one written by Mendenhall (1905) in his paper, The hy- This reservoir [AlpineJ has special interest, not only as the first one of any drology of the . He reported (p. 30): magnitude completed on the . . . Antelope Valley side of the Sierra Madre in Southern California, but because it lies directly in the line of what is known A great fault runs northwest and southeast through the Cajon and San Gor- as the great earthquake crack . . . This remarkable line of fracture can be gonio passes and along the base of the . In the traced for nearly 200 miles through San Bernardino, , Kern and movement along this fracture a portion of the earth's crust north of the San Luis Obispo counties . . . there appears to have been a distinct "fault" present valley was uplifted and now forms the San Bernardino Mountains. along the line [shown on fig. 120], the portion lying south of the line having sunken, and that to the north of it being raised in a well defined ridge.

His sections (p. 32, 36, 68) show a normal fault separating the Although the "earthquake crack" was well known locally and at- mountains from the valley. Imagine Mendenhall's surprise when, tributed to the Fort Tejon 1857 event, it seems that except for Fair- after the 1906 earthquake, his fault was found to be connected to banks, no geologist had described it as a until this 1896 what had been considered a "minor" fault on the San Francisco account, but Schuyler failed to see the now obvious geomorphic Peninsula, some 640 km away. evidence for strike-slip movement. I have found no other references which contain descriptions of Anderson (1899) produced a geologic map and report, "The any portion of the San Andreas fault except as recorded here, until geology of the Point Reyes Peninsula," on the basis of field work the great earthquake of April 18, 1906, made it famous. In this done in 1896-1897. He wrote (p. 143-144): case, as so often happens in geology, the natural catastrophe stimu- lated immediate and intensive study of the fault. At last, the parts of The evidence for faulting along the Baulinas-Tomales Valley . . . [is] to be seen both in topography and in the general stratigraphic and petrologic re- the "elephant" were assembled to reveal a major fracture zone pro- lations. East of the valley . . . the Franciscan series indicate an old topog- ductive of great earthquakes by horizontally oriented elastic re- raphy, yet the transition to the narrow valley bottom is abrupt. The western bound due to accumulative crustal strain. Therefore, in a very real border of the valley is formed by the high, steep ridge of granitic rock. This sense, the San Francisco earthquake introduced a revolution in sci- ridge is in most places capped by Miocene strata . . . Looking at any good entific thought as applied to this fault and to and fault- map of the region ... it seems more than probable that the valley and es- carpment of the Point Reyes Peninsula marks the continuation of faulting ing in general. which is so pronounced at San Bruno Mountain. Actually, it took the earthquake to demonstrate that strike-slip was at least one kinematic mode of displacement on the San An- Anderson produced a good map showing a segment of the San dreas fault. It may have been the first recognition of strike-slip Andreas fault, but he erroneously inferred reversals of dip-slip movement on any major fault. If so, it surely marks a very impor- movement on it. He imagined that the northeast side moved down tant advancement in the understanding of faults. to preserve the Franciscan, then was lifted to remove the Miocene The surface trace of the fault, along which movement occurred at strata, and then moved down again to reveal the granite escarp- the time of the earthquake, was found to extend continuously for ment. He mistakenly assumed that the Franciscan strata were de- nearly 320 km southeastward from Point Arena to San Juan posited on granitic rocks. He connected his fault with Lawson's San Bautista. The largest offset of about 6.4 m was measured on the Bruno fault on the San Franciscan Peninsula, whereas the earth- Point Reyes Peninsula. As noted later, though, this figure is mislead- quake later proved that it was connected to Lawson's (1895) San ing because it is ~ 1.5 m more than any other displacement in the Andreas fault. He also erred in believing that the last movement on epicentral area, and according to Gilbert (Lawson, 1908, p. 71), it his fault did not offset late Pleistocene terrace deposits. was probably augmented by surficial movement. It quickly became Surprisingly, the next description of a segment of the San An- evident that the fault line extended much farther to the southeast; dreas fault was in a paper entitled Reconnaissance of the borax de- compilation of reports, contacts with geologists who were familiar posits of and the Mohave Desert (Campbell, 1902). with the region, and rapid reconnaissance (Lawson, 1906) all con- The author, in traveling through Cajon Pass on his way to the des- tributed to knowledge of its extension. ert, attributed the straight southeastward course of Lone Pine Can- The Mining and Scientific Press included several articles on the yon, and the juxtaposition of unlike rocks across it, to faulting. earthquake shortly after the event. Its publication was immediately

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transferred from San Francisco to Berkeley, and 011 April 28 a sol- The California earthquake of 1906 follows the axis of a very ancient break, icited discussion by Gilbert * (1906) appeared under the title, "The the Portola-Tomales fault, also called the San Andreas fault, first studied, as far as I know, by Dr. John C. Branner in 1891. nature and cause of earthquakes." His brief explanations are the seismological orthodoxy of today, and the following quotation Branner, the principal author of Santa Cruz Folio I <\ 1 (published shows that he had the concept of earthquake generation by elastic by the U.S. Geological Survey in 1909) had mapped the Portola and rebound on faults, which was developed later by Reid (1910). Gil- Stevens Creek faults in his area before 1906 but did not then know bert wrote (p. 272): they comprised a single fault or were connected to Lawson's San Andreas fault. Although Branner's mapping had been as early as Before fracture occurs there is elastic yielding, or strain; that is, the rock is compressed or stretched or bent somewhat like a spring; and when its 1892, it was not published (except as excerpts in a popular article strength is at last overcome the dissevered parts recoil . . . The fracturing by Arnold, 1901, until 1909. Although Jordan (1907) believed producing a tectonic earthquake may be the mere parting of the rock, but that Branner was the first to map a segment of the San Andreas usually there is a slipping along the fracture, constituting a fault. Some of fault, the record indicates that Lawson mapped his segment on the the faults making earthquakes are visible at the surface. The Inyo county San Francisco Peninsula earlier. earthquake in 1872 was associated with a dislocation of several feet, which can still be seen along the western margin of Owen's Valley. Quoting Gilbert in Jordan's book (p. 216-217):

I did not learn until two hours later that a great disaster had been wrought Branner (1906) wrote in the same journal under the title "An au- 011 the opposite side of the bay and that San Francisco was in flames. This thoritative opinion as follows (p. 347): information at once incited a tour of observation and thus began, as far as I was personally concerned, the investigation of the earthquake. A similar Ever since I've been in California I have been making a study of the geology beginning was doubtless made by every other geologist in the State . . . but of the Santa Cruz range of mountains. The work of mapping out the faults organization soon followed, and by the end of the second day . . . men were was completed about six weeks ago. Immediately after the earthquake 1 working in cooperation under the leadership of Professor J. C. Branner, of went out to see if these fault lines had been doing any business. I found, as Stanford University, and Professor A. C. Lawson, of the State University at expected, they had. Where we had located the line on the map was a great Berkeley . . . On the third day after the shock, Governor Pardee appointed a furrow, marking the line of disturbance . . . It showed a lateral displacement State Earthquake Investigation Commission, naming as its chairman — of at least 8 feet. Professor Lawson.

He proposed three theories for the earthquake. In the same book, Tabor' said (p. 259):

The first is that the increase of temperature in the earth, gradually coming The particular fault which caused the earthquake is the Steven's Creek toward the surface, has caused an expansion of the rock and a consequent (Portola-Tomales) fault. It has been traced across the Santa Cruz quad- pressure outward. The second is that rocks which were hot have become rangle by Dr. J. C. Branner and Dr. J. F. Newsom and described by them in cooler and contracted, producing a strain in the other direction. The third is the unpublished Santa Cruz folio of the Geological Survey. that the shifting of the load on top of the earth [by erosion and deposition] produces the pressure. The last quotations I take from Jordan's book are by Fairbanks, who wrote (p. 324): It is revealing to compare this last statement of Branner's on the origin of earthquakes with the much more meaningful one by Gil- As a matter of fact, certain portions of the great rift [San Andreas] have bert, quoted above. been known to the country people living along it for many years. Especially Lawson (1906), on behalf of the Earthquake Commission, pre- is this true of the southern portion, which opened in 1857 .. . Previous to sented a preliminary report in Science (June 29). He described the the earthquake of April, 1906, the writer had traced the rift for fully 400 miles ... It is clear that less than half of the known rift opened during the location and of the "rift" from near Cape Men- recent disturbance. docino into southern California; the extent of ground rupture; the distribution of seismic intensities, and the ground conditions which In explaining scarps along the fault, he said (p. 327), influenced the damage to man-made structures. He wrote (p. 963):

Along the 185 miles of this rift where the movement has actually been ob- The effects of the Tejon earthquake are still visible although it took place served the displacement has been chieflly horizontal on a nearly vertical fifty years ago. Imagination alone can picture the destructive effects of an plane, and the country on the southwest of the rift has moved northwesterly earthquake which could form scarps 100 to 300 feet high. relative to the country on the northeast of the rift. . . in one case a roadway was found to be differentially moved twenty feet . . . The cause of these The first of these statements suggests that Fairbanks was much movements in general terms is that stresses are generated in the earth's crust more impressed with the San Andreas after the 1906 event than be- which accumulate till they exceed the strength of the rocks . . . and they find relief in a sudden rupture. fore, a reaction he certainly shared with the seven other geologists who had described segments of it. In my review of his many publi- cations 011 Coast Ranges geology, the previously quoted statement Referring to the geomorphology of the fault zone, he added (p. 962), (1894) was his only pre-1906 reference to this "great rift." His sec- ond statement, above, indicates his belief, even after the offsets of The scarps can only be ascribed to a rupture of the earth with a relative 1906, that up-and-down (dip-slip) movements were characteristic vertical displacement along the rupture plane. of this fault. In this, and other of his writings, it is obvious that he thought the displacement in 1906 was very minor compared to It is interesting to compare Lawson's reasonable explanation of those which he believed formed 100- to 300-ft (30- to 91-m) scarps. the earthquake with Branner's. But the 20 ft (6.1 m) offset is exces- The foregoing accounts of the local recognitions of segments of sive and Lawson's scarps can be explained by other than dip-slip the San Andreas before 1906, and their interpretations, are surely movement, as Gilbert (in Lawson, 1908) was to explain. not entirely accurate or complete. However, they serve to show that An interesting collection of eight papers, six of which involve these early field geologists, like the blind man guessing the nature of geology, appeared in the book, The California Earthquake of IVO6, the elephant, were really in the dark with respect to the fault's edited by Jordan (1907). Jordan stated (p. 5): length. Obviously, it took the earthquake to reveal its continuity

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and to first indicate, as a revolutionary scientific concept, its Lawson must be referring here to his own work (1893), but he tectonic importance. Following the earthquake, many geologists may have overlooked the fact that he first used the name, "San An- learned much about this great structure and quickly wrote scien- dreas fault," in a later publication (1895) for what he had probably tifically good or bad preliminary accounts of it. However, it was mapped in 1891 and first described in 1893. not until the report of the California Earthquake Investigation Lawson's summary statements on structure (p. 17 — 19) included Commission (Lawson and others, 1908, and Reid, 1910) that these a discussion of faults in California. Some of these were named, lo- facts and accompanying interpretations were systematically pre- cated, and very briefly described. Map 1 of the Atlas accompanying sented. the report is a fault map of of the State of California, and Plate 15 (opposite p. 8) is a geomorphic-geologic map of the San Francisco THE EARTHQUAKE COMMISSION REPORT TO 1926 Peninsula, showing faults, including the type locality of the San Andreas. This first fault map of California (Lawson, 1908) showed Three days after the San Francisco earthquake, the Earthquake few faults compared to maps by Willis and Wood (1922) and Jen- Investigation Commission of eight highly qualified scientists was nings (1975). The map of the San Francisco Peninsula was repro- appointed by Governor Pardee to study and report on the effects duced from an earlier report (Lawson, 1895). Lawson wrote (p. and causes of the earthquake. The chairman of the Commission, 18-19): Professor A. C. Lawson, was responsible for producing a two- volume report entitled, The C.alifornia Earthquake of April IS, The most interesting fault traversing the Peninsula of San Francisco is the 1906. Volume 1 (1908) by this same title, was written largely by San Andreas fault, on which movement was renewed on April 18, 1906, causing the earthquake. Lawson during the winter of 1906—1907. It includes descriptions of the geomorphology, and what little was known of the geology, It [the San Andreasl is only one of many faults, on all of which in past time there have occurred many differential movements, each productive of an along almost the entire length of the San Andreas fault, sys- earthquake. tematically arranged descriptions of offset ground and man-made structures along the activated fault trace, and 146 illustrations, Before the San Francisco event, this fault had been described and mainly photographs of ground disturbances and damaged build- mapped by Lawson (1 893, 1895) as a minor one on the peninsula, ings. (The term, "rift," used consistently in the report, is no longer but, of course, after the earthquake, it became "interesting." We appropriate). Volume II, entitled The Mechanics of the Earth- now know that creep can occur along faults without the generation quake, written by Professor H. F. Reid, included an analysis of of earthquakes, that few active faults are characterized by ground motions and instrumental records of the earthquake. It was sufficiently large and sudden slips to cause significant earthquakes, in this volume that the classical, and still applicable, elastic- and that many faults are inactive. rebound theory of earthquakes was developed. An Atlas (1908) of In Lawson's 22-page discussion of The San Andreas Rift as a 25 maps, including the location of the fault trace on U.S. Geologi- Geoniorphic Feature, which progresses in geographic segments cal Survey topographic quadrangles and copies of 92 seismograms from near southeastward to the , he from stations around the world, accompanied the report. The orig- stated (p. 26, 27, 29): inal report was financed and released by the Carnegie Institution of Washington, D.C., as Publication 87. Fortunately, it is again avail- From Shelter Cove to near Point Arena, the Rift, if continuous, lies beneath able in the reprinted Carnegie Institution edition of 1969, edited by the waters of the Pacific ... In the vicinity of Fort Ross, the geomorphic the late W. W. Rubey. forms of the Rift are particularly well exemplified . . . low ridges . . . mark its course . . . Behind the ridges and scarps are ponds and small swamps. The report of the Commission was a prominent "bench mark" in Some of the streams follow the Rift ... It is also a remarkable fact that the ongoing study of the San Andreas fault, because it presented the altho on the east side of the defile [Bolinas-Tomales valleysjthe Franciscan first comprehensive description of the geomorphology and the then rocks constitute ... a thickness of several thousand feet, this entire series known geology of this recently discovered structure. The foregoing . . . is. . . absent between the Monterey and granitic rocks on the Peninsula section of this history culminated with the discovery of an active in the immediate vicinity [on the west side of the defile]. This indicates clearly that in pre-Miocene time the peninsula mass had been uplifted on a fault zone as revealed by a 320-km-long zone of ground breakage fault... so that granite was brought against the Franciscan and denuded of accompanying the San Francisco earthquake, whereas this section its unconformable mantle of sedimentary strata before it was [again] sub- takes off from the solid base of the Commission's report. merged to receive deposits of Monterey time. It is also clear that inasmuch I begin here by quoting an introductory statement by Lawson (p. as there is a great volume of Monterey shales on the . . . seaward side of the fault line, and no trace of the same formation of the mainland to the east of 2 of the report): the fault line, one of two things must have happened. Either the sub- mergence which permitted the deposition of the Monterey shales was The cause of the earthquake . . . was the sudden rupture of the earth's crust confined to the Peninsula and was effected by a downthrow on that block or along a line . . . from the vicinity of Point Delgada [Humboldt Countyl to a the same fault as that upon which it had earlier been upthrust ... or if the point in San Benito County near San Juan; a distance, in a nearly straight regions on both sides of the fault were submerged together, then in Post- course, of about 270 miles. For a distance of 190 miles from Point Arena to Miocene time the east side of the fault was uplifted into the zone of erosion San Juan, the fissure formed by this rupture is known to be practically con- and denuded of its cover of Monterey . . . There is no escape from one or tinuous . . . This line is marked by features due to former earth movements the other of these conclusions . . . The trace of this ancient fault is also the and will be referred to in a general way as a rift, the term being adopted line of the modern Rift. from the usage for analogous features in Palestine and Africa. To distin- guish it from other rifts of similar origin, it will be referred to more spec- ifically as the San Andreas Rift, the name being taken from the San Andreas In regard to the first question above, Curray and Nason's (1967) Valley on the peninsula of San Francisco . . . where its diastrophic origin marine seismic profiles indicate that the San Andreas is continuous was first recognized in the literature. The plane or zone on which the rup- from Point Arena to Shelter Cove. The last quotation indicates that ture took place is . . . nearly vertical; and upon this vertical plane there oc- Lawson followed, or led, Anderson (1899) in explaining the differ- curred a horizontal displacement. . . The displacement was such as to cause the country to the southwest of the rift line to be moved northwesterly rela- ence between stratigraphic sections on opposite sides of the fault, tive to the country on the northeast side of that line. The differential dis- whereas, now they are explained by many miles of horizontal placement in a horizontal direction ... in many places measured over 15 (strike-slip) displacement. Anderson followed hjs professor's error feet, and in one place as much as 21 feet. (Lawson, 1 893) in assuming that Franciscan strata had to be depo-

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sited on granitic basement, and neither of them could see the "es- It is likely that Fairbanks had seen more of the fault from its cape" from up and down (dip-slip) movements on the San Andreas. northern segment in Humboldt County to its uncertain location in Lawson continued (p. 35 of the report): the than any other geologist. However, the generalization that "important scarps mark the rift throughout its From the top of these cliffs [Mussell Rock] ... the course of the Rift as far whole course" is too sweeping; scarps like these bounding the Elk- as is marked by a line of shallow . . . depressions, ponds horn Hills, and most others along the rift, did not come into exis- and low scarps. This portion of the modern Rift was recognized as such in 1893. tence through any one movement of tens to hundreds of feet, or even by repetitive dip-slip movements.

This last sentence indicates that Lawson was not surprised that In describing the fault within the San Emigdio Mountains and on ground breakage had occurred here in 1906. Although he had rec- the north side of the San Gabriel Range, Fairbanks stated (p. 42- ognized that movement on this fault was post-Pliocene (1893), 43): however, he definitely considered it to be a relatively minor fault on Santiago Canyon marks a great fault of earlier times. Soft Tertiary forma- the San Francisco Peninsula (1895), and he probably was surprised tions are faulted down thousands of feet upon the south side of the canyon, that the surface dislocation was on it. while upon the north appear the steep granitic slopes of the western spur of The Portola—Steven's Creek segment of the fault is very briefly San Emedio Mountain [San Emigdio Mountains] . . . The long desert waste described by Lawson, although according to Branner (1906), Jor- plain [Antelope Valley] leading up to the foot of the mountains on the south (San Gabriel Range) exhibits a strikingly interesting feature. It is not con- dan (1907), and Tabor (1907), this area had been mapped by tinuous across the line of the Rift, but shows a break with the uplift upon Branner and his Stanford University associates long before the the lower [north] side. The amount of displacement appears to be between earthquake. The question arises as to why Branner did not, as a 200 and 300 feet. member of the Commission, write this section of the report? My guess is that institutional chauvinism and professional jealousy These quotations show that Fairbanks assumed, from strati- motivated Lawson to avoid using Branner, although he did use Lar- graphic and topographic cross-fault relations, that movements on sen's (University of California) description (p. 36—37) in the next the fault were primarily up and down (dip-slip), whereas we know southerly segment. horizontal movements (strike-slip) juxtapose unlike stratigraphic The southern portion of the fault, 480 km long and less well sections and unequal ground elevations. Again, this illustrates the mapped, was described by H. W. Fairbanks (p. 38-47). He began confusion, extant even today, between the concepts of fault sep- (p. 38): aration (geometry) and fault slip (kinematics). Fairbanks described the fault on the south side of the San Ber- The earthquake of April 18, 1906 opened and displaced the walls of the old nardino Mountains as follows (p. 44-45): fault along the Rift as far south as the town of San Juan in San Benito County ... at a point midway between the [San Juan River] bridge and San On the west side of Diablo [Devil] Canyon there is a double escarpment in Juan, there is shown in a broken fence a horizontal displacement of 4 feet. the gravels, both apparently being due to movements along the Rift. There is a much dissected fault cliff 200-300 feet in height. Plainly traceable in the In describing the fault south of the San Benito Post Office, he front of this cliff is a small break, possibly made in 1857. No definite infor- wrote (p. 39): mation could be gained as to whether the earth opened here at that time, but reports say the earthquake was very severe, throwing animals from their A fertile valley . . . appears to have been formed by subsidence, while on the feet, etc. . . . The southern portion of the San Bernardino Range lying be- southwest is an abrupt ridge 200 feet high and fully a mile long. The ridge tween Mill Creek and the Conchilla [Coachilla] Desert appears to have un- without doubt has been produced by faulting. Its abrupt northeastern face dergone great disturbance at a recent date. As a consequence, erosion has- and long, gentle, southwesterly slope suggest in a remarkable manner the been rapid and extensive, and surface features which further north made the great fault blocks of the west, such as the Range. Rift easy to follow have in this region been almost completely obliterated.

This statement by Fairbanks indicates that he, and most other Here is another indication that Fairbanks thought scarps several geologists, interpreted the topographic scarps in the fault zone as hundred feet high could accompany catastrophic earthquakes. Re- having been produced by dip-slip movements. It would be interest- cent study (Sieh, 1978) has shown that ground "opening" probably ing to know how Gilbert would have interpreted these scarps, con- did not occur here in 1857 (actually, opening or rifting along the sidering his recognition that strike-slip movement at the time of the San Andreas fault is no more common than "overlapping" with the earthquake produced apparent vertical movement of a sloping formation of the so-called pressure ridges). ground surface (in Lawson, 1908, p. 72). Fairbanks continued (p. 46-47): Fairbanks continued (p. 41 -42), It was thought that the Rift, if continued on southeasterly, would be found crossing the . . . skirting the [north-] eastern base of the San Jacinto Range; bur this proved not to be the case. Instead, it was found The people living along the Rift for 150 miles southeastward from Cholame to turn more and more easterly and finally to extend parallel to the pass Valley tell wonderful stories of openings made in the earth by the earth- without reaching it ... It may be reasonably assumed, then, from our best quake of 1857 ... It [the Rift on the southwest side of the ] knowledge, that the southern end of the great Rift is to be traced for an is marked by a distinctly steeper slope . . . showing that an uplift of 30 to 50 unknown distance along the base of the mountains bordering the Salton feet took place on the west side . . . This ridge [Elkhorn Hills] is clearly a Basin on the northeast, in all probability dying out. fault block, now separating the Carissa [Carrizol Plain from Elkhorn Plain. It probably originated during some one of the earlier movements along the Rift; in fact it is reasonable to suppose that it is of the same age as other Fairbanks, others of his time, and even the geologists of today, important scarps which mark the Rift throughout its whole course, and have tried to trace the San Andreas fault through the San Gorgonio which came into existence as a result of some mighty movement opening the Pass and farther to the southeast; although several faults have been earth for several hundred miles . . . Plainly visible along the steep front of mapped, there is uncertainty about which specific one is the San the line of hills described are the lesser ridges and hollows produced during the last violent earthquake in this region, probably in 1857 . . . The larger Andreas, sensu stricto. scarps belong to some ancient disturbance, while the last one, probably dat- After a one-page description of the then known earthquake pro- ing from 1857, is marked by features comparatively insignificant. ducing San Jacinto fault, Lawson concluded this section of the re-

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port with a five-page "Review of salient [geomorphic] features." passes, where geomorphology and geology so clearly show evi- He wrote (p. 52): dences of faulting. However, they did not have aerial photos or were they able to fly between Los Angeles and San Francisco; The Rift is known from Humboldt County to the north end of the Colorado geologic mapping, especially in southern California, had essentially Desert . . . and in the usage of the term [Rift] it has been understood as not commenced until about 1910 when regional mapping for oil terminating at a point where it eluded field observation. But it is by no exploration became greatly accelerated. means certain that, as a larger feature, it does not extend far to the south . . . It thus seems not improbable that the three great earthquakes of California, Studies of two well-mapped areas which included segments of Chilpancingo [near Acapulco, ] and Jamaica may be on the same the San Andreas fault became available as U.S. Geological Survey seismic line which is known in California as the San Andreas Rift. Folios soon after the San Francisco earthquake. Folio 163 by Bran- ner and others (1909), covered the Santa Cruz 30-minute quad- Perhaps Lawson did not agree, as he seldom did, with Fairbanks rangle, and Folio 193 by Lawson (1914) covered the area im- on the termination of the San Andreas, or perhaps he only wanted mediately to the north on five 15-minute quadrangles, including the to point out that his speculation on an extension of the fracture San Francisco and Point Reyes peninsulas. Although Lawson and zone was just as good as the speculation by Fairbanks. Present Branner had mapped segments of the San Andreas fault long before mapping and interpretations favor Fairbank's model, but the loca- 1906, apparently neither knew of its continuity between their areas tion and mechanism of the fault's termination have not yet been until after the earthquake. fully resolved. I quote from Folio 163 (Branner and others, 1909, p. 9): The next section of the report (p. 53-113) comprises descrip- tions, progressing from north to south, of the April 18, 1906, The most important structural feature of the quadrangle is the great fault ground movements and their effects along the San Andreas fault. passing through Portola. This fault which extends many miles beyond this These detailed accounts are accompanied by many figures and quadrangle is known throughout its length as the San Andreas fault... It is locally referred to as the Portola and Stevens Creek fault . . . The San An- photographs of scarps, ridges, trenches, and ponds, and of offset dreas fault forms most of die dividing line between the Tertiary rocks to the roads, fences, railroads, tree rows, pipelines, dams, bridges, tun- southwest and the Cretaceous and Franciscan rocks to the northeast. It ap- nels, buildings, etc. (A problem is posed by photos; Plates 64B and pears probable that this fault line has been a line of weakness since early 65A show several feet of left-lateral offset.) Tertiary time . . . While many movements have probably occurred along it, sometimes with downthrow on the east side and sometimes on the west, the An especially thorough account of disturbances which occurred sum total of these movements has resulted in an uplift on the east with a at the time of the earthquake was written for the report by Gilbert. downthrow on the west. . . The total uplift on the east is not known. Judg- His discussion (p. 66-91) was based on his own observations ing, however, from the thickness of Tertiary rocks on the west which are along the - segment of the fault. It is not represented on the east side of the fracture, the displacement must be several thousand feet. accompanied by photographs and 13 figures. His analyses and in- terpretations were superb. His many measurements of offsets along the fault varied from 3 to 4.7 m of right-lateral slip, and one offset It is significant to note that Branner also assumed that the princi- of 6.1 m, which he thought must have been augmented by surficial pal component of movements on the San Andreas fault were verti- movement. Gilbert said (p. 72): cal. He described four other important northwest-trending faults in the quadrangle on which he thought vertical throws of ~ 610 m had The phenomena of vertical displacements are in general so irregular as to occurred; he showed up-and-down arrows on these and the San indicate they were chiefly determined by surface conditions. Where the Andreas fault on the cross sections; he showed no strike-slip arrows ground sloped toward the northwest the horizontal throw caused an appar- along any of the faults on the geologic map. One wonders if Bran- ent vertical downthrow to the northeast [side of the fault], ner would have considered his Portola-Stevens Creek fault zone to have been the most important structure on the Santa Cruz Quad- Gilbert may have believed that earlier movements on the fault rangle if the San Francisco earthquake had not occurred before the were mostly vertical (dip-slip), but this statement shows that he un- publication of Folio 163. derstood the difference between fault separation and fault slip. (I Furthermore, he stated (p. 9): wish he were here to tell us what he thought then about pre-1906 movements.) The earthquake of April 18, 1906, is supposed to have been caused by a In this history of knowledge about the San Andreas fault, the movement which took place at that time along the San Andreas fault. The Commission's report is a milestone, because it records and confirms displacement was chiefly horizontal, amounting to a maximum of 8V2 feet what was revealed by the earthquake and systematically documents within this quadrangle, the northeast side moving relatively to the south- east. the San Andreas fault as a long and tectonically important crustal fracture. The geomorphic aspects, both of terrain disturbances de- veloped at the time of the earthquake and those caused by a mul- Here the word "supposed" is revealing, as it seems to indicate titude of earlier displacements are thoroughly presented, and they that Branner had difficulty in accepting strike-slip on a fault which revealed for the first time much about the San Andreas fault. On the so obviously had, according to his interpretation of geologic sec- other hand, the geologic aspects, except for the tions, up-and-down movements. It is interesting to note that there region, were essentially unknown in 1906 and therefore had to wait are no references to previous geologic work in Folio 163, maybe for geologic mapping and interpretations concerning the charac- because most of it had been done by Lawson and his students at the teristics and displacement history of this great fault. The earth- University of California. Apparently Branner preferred the name quake established the fault on the ground and in the minds of "Portola-Tomales" over "San Andreas" after these segments were geologists. The immediate field work by the few available connected by the 1906 ground breakage (Jordan, 1907), and geologists culminated in the report of the Commission, which perhaps also because ol: professional and institutional jealousies. paved the way for continued earthquake and San Andreas fault Quoting from Lawson's (1914) San Francisco Folio 193 (p. 16): studies. It may seem odd that this major, and now so obvious, San In later Quaternary time, subsequent to the large displacements that are Andreas fault had not been previously recognized by the slow- represented by the San Bruno fault, there began the movements which are traveling geologists of the late 19th Century, especially in their still in progress but are as yet relatively small and are characterized by a numerous trips through the San Gorgonio, Cajon, and Tejon great excess of their horizontal over their vertical component. In the

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Tamalpais quadrangle the trace of the San Andreas is coincident with that In the Bulletin on the geology and oil prospects of the Salinas of the San Bruno fault, but in the area south of the Golden Gate the line of Valley-Parkfield area, English (1919) implied vertical movement the San Andreas is separate and divergent from the older line of dislocation. on the San Andreas when he wrote (p. 246-247):

In the above quotation, Lawson introduced an ambiguity by giv- Toward the north ... the Vaqueros formation and the Santa Margarita (?) ing one fault name for the older inferred dip-slip movements and formation, which are well developed on the southwest side of the fault, are another name to the same fault with the late Quaternary strike-slip absent on the northeast side . . . Sometime before the deposition of the displacement. Obviously he agreed with Anderson (1899) here, and upper Miocene sediments ... the area [northeast of the San Andreas! was uplifted and the Vaqueros and Santa Margarita (?) formations were entirely probably nearly all geologists of that day, perhaps excepting Gil- eroded away. bert, in confusing fault separations in geologic sections with fault slips. Lawson got into further trouble by assuming the San Andreas Pack (1920) showed the San Andreas fault along the southwest fault on the San Franciscan Peninsula to be a minor structure com- side of his geologic map of the Midway-Sunset area (southwestern pared to the San Bruno fault, as indicated by his fault map (p. 15). I ) and he stated (p. 61): am guessing that he would have been less surprised if the ground breakage accompanying the 1906 seismic event had been on his San The largest single structural feature in the San Emigdio Mountains is the Bruno, rather than on the San Andreas, fault. San Andreas fault, or the "earthquake line," as it is commonly known be- Another phase of geologic mapping in areas transected by the cause of the fact that movements on this fault farther north were the cause San Andreas fault was largely done by the U.S. Geological Survey of the San Francisco earthquake . . . Movements along the fault have been profound and in the area shown on the map [Plate II Geologic Map and and published in Bulletins and Professional Papers. The principal Sections] have resulted in vertical displacement that aggregates many hun- objective of this work was the presentation of regional structure dreds or perhaps several thousand feet ... on the east branch of Santiago and stratigraphy to help the petroleum industry select areas for Creek near the southern edge of the area shown on the geologic map . . . the more detailed studies, leading to exploratory drilling. These Bulle- Mesozoic granite on the north side of the canyon is in fault contact with Miocene sands and gravels on the south ... it seems possible that most of tins, most of which were published between the years 1908 and the faults are normal. 1924, served their purpose admirably. However, mapping of seg- ments of the San Andreas fault where they occurred was only inci- These and other statements indicate that geologists of this era dental to the economic objective, and scant discussions of the fault believed the principal movements on the San Andreas were vertical, were made only occasionally. As will be evident in the following although all of them knew about horizontal displacement at the quotations, these geologists assumed dip-slip displacements to ac- time of the San Francisco Earthquake. Presumably they thought the count for cross-fault stratigraphic differences, although knowing 1906 displacement was atypical. about strike-slip on the San Andreas accompanying the 1906 Willis (1921) pioneered in air reconnaissance along the San An- earthquake. dreas fault from San Francisco to Tejon Pass and said (p. 139): Arnold and Johnson (1910, p. 102) in their Bulletin 406 on the oil possibilities in the Midway-Sunset area (on the west side of the 1 conclude that the airplane can be used to advantage as a means of rapid southern San Joaquin Valley) said: reconnaissance to map large structural features.

It [Temblor Range] is skirted along its southwest side by the great world Vaughan (1922) wrote in his paper on the geology of the San structure known in the United States as the San Andreas fault zone . . . Bernardino Mountains (p. 399), Definite evidence of horizontal movement [on the San Andreas fault] has been found in the region, atone point of over 400 feet. . . Elkhorn scarp . . . is undoubtedly due to the dropping down of the or elevation The most interesting fault in this region is the San Andreas, since it has been of the Elkhorn Valley of about 200 feet. the focus of many movements resulting in severe earthquakes, notably those of 1857 and 1906 . . . just west of Stubby Canyon the dip of the fault plane is 70° to the north, so that schists on the north override the fanglomerates to This statement allows speculation about the 122 m of horizontal the south. Since the schists are older, it is apparent that the fault [San An- movement. I assume the evidence was an offset drainage line, many dreas] is a thrust. of which are clearly seen along this stretch of the fault, but did they believe the 122-m displacement occurred at one time, either before Thus, Vaughan in this 1922 report, concluded that the principal or with the 1857 earthquake? They did not say, nor did they men- movement on the San Andreas is up and down (dip-slip) on the tion that earthquake, which is now interpreted as being due to basis of fault separations observed in geologic cross sections. ~9.1 m of right-slip on the San Andreas fault (Wallace, 1968; Sieh, A paper by Kerr and Schenck (1925) on the faults in San Benito 1978). This statement also reveals that Arnold and Johnson County covers an area which is divided by the San Andreas fault thought that scarps had to be the result of vertical components of (map opposite p. 473). They pointed out the great difference in movement on the faults. rock types and stratigraphy on opposite sides of the San Andreas, Pack and English (1915) reporting on the oil possibilities of a but they did not specifically relate these sections to movement on large area between the San Joaquin and , California, the fault. They did describe thrust faults and folds which trend said (p. 135): more westerly than the northwest-trending San Andreas and re- lated this structural pattern to the direction of horizontal move- ment on the San Andreas, like that at the time of the San Francisco The dominant structural feature in this part of the Diablo Range is the San earthquake. In a footnote (p. 478), they repeated a statement made Andreas fault, which trends diagonally across the region mapped, separat- ing it into two parts, which exhibit two distinct types of structure. The dis- by A. C. Lawson at the 1924 Geological Society of America meet- similarity in the stratigraphic record on opposite sides of the fault. . . shows ing: pronounced movements have taken place along it since at least as far back as middle Miocene time. The movements along the line farther north, which The horizontal displacement [on the San Andreas] is unknown, but may be caused the earthquake of April 18, 1906, were almost wholly horizontal, as great as twenty miles. but lack of the Franciscan, Cretaceous, and Vaqueros formations and the presence of granite Ion the southwest side of the fault] seems to indicate there was once very considerable elevation [and erosion] ... of the mass I believe that Lawson must have been referring to Noble's lying west of the fault relative to that lying to the east of it. suggestion of 24 mi (38 km) of strike-slip on the San Andreas fault

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in southern California, because Lawson was on the Carnegie In- principal component of cumulative slip on the San Andreas fault stitution's committee on seismology, and this institution published could be horizontal (strike-slip). Thus, by implication or direct Noble's (1926) paper. Lawson apparently did not say then, or as statement, strike-slip movement on the San Andreas fault at the far as I know at any time later, whether he subscribed to so many time of the San Francisco earthquake was considered to be anoma- miles of horizontal movement on the San Andreas. 1 doubt that he lous, or even the beginning of a new kinematic mechanism. How- believed in the possibility of miles of offset on the San Andreas ever, after Noble's (1926) paper and the controversy it introduced, fault, but knowing Lawson, I can guess that he was trying to sur- some renewed interest was focused on the San Andreas, although prise and shock the audience. Certainly his associates at the Uni- obviously not so strong and immediate as that following the San versity of California, for example, Taliaferro, did not subscribe to Francisco earthquake. such movement on the fault. It seems to me that the next paper quoted here should have been NOBLE'S PROPOSAL TO 1953 the "new light" in determining cumulative strike-slip on faults. Although this new approach, or method, was not applied to the San The next era in advancing understanding of the San Andreas Andreas fault, it may have influenced the analysis by Noble (1926) fault is considered here to begin with Noble's'' suggestion (1926) of with which the next section of this history begins. 38 km of cumulative horizontal displacement along the fault. It is The first published suggestion of several miles of cumulative the first published evidence for miles of movement and, although strike-slip on any fault in California, or perhaps elsewhere, may short, tentative, and of minor impact compared to the San Fran- have been made by Vickery'" (1925). In his 20-page structural cisco earthquake, it introduced a revolutionary and fruitful idea analysis of the Livermore area, 64 km southeast of San Francisco, about the character and history of the fault. Consequently, it stimu- he claimed (p. 611-612): lated new studies, which gradually produced new information, which in turn generated some controversies and thereby even more The strike shift of the structural and stratigraphic units shows the direction intensive studies. and amount of movement on the Sunol [CalaverasJ fault. The Briones for- In this very modest report to the Carnegie Institution's Advisory mation is a series of sandstones and shell-breccia beds whose phases may be easily recognized. It overlies the Temblor formation, which likewise has Committee on Seismology, Noble effectively described the geology distinctive phases. On the westerly side of the Sunol fault northwest of of an 80-km-long and 9-km-wide area straddling the San Andreas Dublin, the Briones formation is characterized by shell-breccia reefs, and on the north side of the . the Temblor sandstone. A similar series lies on the easterly side of the fault He stated (p. 418): southeast of Sunol. In fact the two areas are so alike that Astrodapsis bre- werianas (Redmond) is found only in the northeastern portion of each. Measuring between corresponding points, namely, the southerly intersec- Although the San Andreas fault runs for some distance near the northern tion of the Briones contact with the fault, the strike shift is 12 miles. Be- base of the San Gabriel Range, it does not actually bound the range, for it tween two lower Miocene localities characterized by the abundance of Pec- crosses the range at an elevation of 6,800 feet between Rock Creek and ten propatulus (Conrad) the measurement is 13 miles, and between two (the Cajon Pass. The initial uplift of the Range did not take place upon the main only two) Pliocene rhyolitic localities, it is 9 miles. San Andreas fault, but, rather, upon faults that branch from the San An- dreas zone. The planes of these branching faults, wherever exposed to ob- servation, are thrust planes which dip steeply southwestward into the I have seen no published evidence which contradicts Vickery's in- mountain mass in such a way that the older crystalline rocks of the range terpretation; apparently it was ignored. I am inclined to believe that override the younger sedimentary rocks at the base of the range. the unorthodoxy of miles of strike-slip on a fault was considered unworthy of written comment by the University of California au- This is probably the first direct statement in the literature which thorities on the area. Perhaps they ignored this paper as a ridiculous does not call upon the San Andreas fault to effect uplift of the San interpretation of a fault by a Stanford student poaching on their Gabriel Mountains. territory. If Vickery received no reaction to his inference of a 21 -km He also suggested (p. 420): offset on the Calaveras fault, he must have been greatly disap- pointed, especially since such a new concept was testable by The distribution of a certain Tertiary rock masses along the master fault affords a suggestion that a horizontal shift of many miles has taken place geologic field studies. I guess that his methodology influenced along the rift. On the north side of the fault, near Cajon Pass, a small block Noble (1926), and I know that it influenced Hill and Dibblee of strata lithologically similar to beds in the Martinez formation at Rock (1953) in their analyses of cumulative slip on the San Andreas fault. Creek is associated with Mint Canyon Beds [Miocene terrestrial strata]. The Except for the comprehensive Report of the Earthquake Com- only other exposure of Martinez associated with Mint Canyon beds any- where in the region lies on the opposite side of the fault at Rock Creek 24 mission (1908, 1910), very little in the way of geologic studies, miles northwest of the locality in Cajon Pass ... it thus appears possible specifically directed to the San Andreas fault, appeared in the that horizontal movements along the fault have dragged the rock masses geologic literature until 1926. As more and better topographic map north of the fault to the southeast in relation to those southwest of the fault coverage became available, areas that included the San Andreas . . . The evidence just cited, however, is not convincing, and is certainly not were mapped. As indicated above, most of these studies were made definite enough to amount to proof. to facilitate exploration for petroleum. The fact that very little at- tention was given to the San Andreas fault for many years after the Clearly, Noble had doubts about 38 km of movement on the San Commission's report may have been because geologists generally Andreas, and, as we shall see, he apparently gave up the idea a few believed that the last words had been written about it. In this con- years later (Noble, 1933). Still later, however, he developed evi- nection, they may have followed Jordan (1907), who said (p. 51): dence and support for more than 48 km of horizontal offset on this segment of the fault (Noble, 1954). The final report of this commission [Lawson, 1908] should leave no impor- R. T. Hill (1928), in his book entitled Southern California and tant question in doubt. Los Angeles Earthquakes wrote (p. 175):

Furthermore, as I have emphasized by frequent comments on Vertical movements along the Southern Section of the San Andreas Rift selected quotations, essentially none of the interpretations, except have resulted in the production of the master physiographic highlands, val- Lawson's comment quoted above, indicated the possibility that the leys and other lineaments of Southern California. To them are due the

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sharp, rectilinear scarp-lines of the northeast side of the San Gabriel High- Cenozoic eras, which explains the presence or absence of stratig- lands [Mountains! and the southwest side of the San Bernardino raphic units across them. Mountains. Clark was afflicted with the delusion, common then and now, that separations (geometry) revealed in geologic cross sections re- Hill knew about strike-slip on the San Andreas at the time of the sulted from dip-slip movements (kinematics) on faults. We now be- San Francisco earthquake, and he refers to Noble's work on the lieve that most of these cross-fault relationships can be explained north side of the San Gabriel Mountains. However, his emphasis more satisfactorily by strike-slip in order to juxtapose unlike rock was on vertical movements to produce the attractive landscape and sequences. In this connection, as we shall see later, Ralph Reed climate in southern California. His objective was to argue that (1933, p. 100-101) believed that intermittent periods of folding earthquake risk in Los Angeles was minor, contrary to some other produced the up-and-down movements, which explained the prox- opinions, because the only faults which could generate large earth- imity of unlike stratigraphic sections better than Clark's block- quakes, the San Andreas and San Jacinto, were too far from Los faulting hypothesis. Clark argued, in one of his last papers (1935), Angeles to cause great damage. against Reed's criticism of his hypothesis. However, neither Clark He also stated (p. 225): nor Reed entertained the possibility that is now favored: explaining adjacent unlike stratigraphic sections by strike-slip faulting. The recent movements [referring to strike-slip on the San Andreas in the King (1932) in his Structural geology of the United States, writ- Cajon Pass area and elsewherel are trivial in comparison to the greater ones ten for the 16th International Geological Congress, said (p. 51): of the several epochs of the late Pleistocene and, in my opinion, are but the surviving after-effects thereof. It is a grave mistake to believe that the movements are as active now as they were in past epochs when the rhythms Movements on the San Andreas fault have been both horizontal and verti- of movements [ vertical] were at their apogee. cal. The vertical movements differed in direction at different places along the fault.

This quotation indicates to me that Hill believed strike-slip on Obviously, King then believed that vertical movements on the San the San Andreas was a geologically new mode of displacement, and Andreas were indicated by topograhic profiles and geologic sec- that deformational forces were diminishing. tions. He was familiar with Noble's (1926) work, having visited Wood and Bulwalda (1930) wrote a paper entitled "Horizontal him in the field, but there is no indication here that he (King) then displacement along the San Andreas fault in Carrizo Plain, believed that there had been 38 km of strike-slip on the fault. I California," in which they stated (p. 75): guess that King believed vertical movements, and perhaps reversals The evidence indicates clearly that the block west of the fault [San AndreasJ of these movements, were more important than horizontal ones, has moved northward relative to the eastern block at least several thousand and that perhaps King helped talk Noble out of the idea of miles of feet in very recent time; the [offset] drainage courses are very young fea- horizontal displacement. King accepted, in this paper, the figure of tures. Total horizontal displacement of much greater magnitude, measured 6.4 m for the maximum right-slip on the San Andreas in 1906. This in terms of many miles, or in tens of miles, is thereby strongly indicated. acceptance has helped to perpetuate what is probably an erroneous fault displacement according to Gilbert's own work and statement These authors were obviously impressed with Noble's (1926) (Lawson and others, 1908, p. 72), whereas 4.7 m of offset was the suggestion of 38 km of horizontal movement along the San An- confirmed amount. dreas fault. Seeing gemorphic evidences for sense of slip in 1857 Loel and Corey (1932) wrote a comprehensive book-long paper and before, plus believing in uniformitarianism, they could safely on the Vaqueros Formation of California, comprising descriptions conclude that cumulative right-slip of many miles had occurred on of rock facies and their distributions, and the taxonomy of the the San Andreas fault. moluscan assemblages, with excellent photographic plates of Clark" (1930) wrote the long paper, "Tectonics of Coast selected species. Of interest in the context of this history is their Ranges," in further application of his hypothesis of 1929 that in- paleogeographic map (opposite p. 50) which depicts the lower dividual fault-bounded blocks had bobbed up and down to receive, Miocene sea of the southern San Joaquin Valley extending west- or be denuded of, rock units during Mesozoic and Cenozoic time. ward directly across the San Andreas fault. This, Reed's (1933) He stated in the 1930 paper (p. 819): maps, and most other paleogeographic and paleogeologic maps are misleading because they fail to take into account, by palinspastic The Coast Ranges of California are formed along a series of old [Mesozoic] faults, here referred to as primary. . . . The uplift of the positive blocks has techniques, the miles of horizontal offset on the San Andreas and been mostly vertical. In the writer's opinion there is no good evidence of other major strike-slip faults in California. great horizontal movements of positive and negative blocks. Noble (1933) in his Excursion to the San Andreas Fault and Cajon Pass, written for the 16th International Geological Congress, Clark explained the great contrast in the sequence of formations said (p. 11): as seen on the two sides of the San Andreas fault, by reversals of throw on the fault (p. 778). The fault is a very old line of weakness along which movements appear to He said (p. 780): have been partly horizontal and partly vertical . . . which movements have recurred through much of the pre-Tertiary. Reversals of movements on the major faults has been a common phenomena |sic] throughout the Coast Ranges. Noble did not refer to his 1926 paper on mention his suggestion of 38 km of horizontal movement on the fault. His cross sections His map (opposite p. 770) shows 57 primary faults in California show arrows for up-and-down movements, and no arrows for and the names of 24 crustal blocks separated by them. The San An- horizontal movements are on the map (PI. 3, opposite p. 12). Had dreas fault bounds one side of many of these blocks. His cross sec- he given up the idea of miles of strike-slip on the San Andreas fault, tions (Pis. 17 and 18) show up and down arrows on all of the faults, and if so, why? I can only guess that he could not withstand the including the San Andreas. According to Clark, most of these 57 opposition of several good geologists, such as P. B. King, R. D. primary faults suffered reversals of throw during Mesozoic and Reed, and A. C. Lawson. However, Noble later (1954) presented

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good evidence and argued strongly for at least 48 km of right-slip Andreas. 1 guess that, at this time, most California geologists ac- on the fault. cepted most of Taliaferro's firm, but mostly wrong, conclusions. Reed:: (1933), in his book Geology of California, wrote (p. (Further comments follow quotations from his 1943 and 1951 pa- 11-12, 38): pers.) Eaton (1939), describing the geology of Ridge Basin, California, The San Andreas fault, which has been famous since 1906, has been ac- concluded (p. 520): cused of most of the irregularities in the structure and constitution of the whole province. Its existence, at least, is certain . . . There is much evidence The approximate amount of horizontal throw along the San Andreas rift that during recent time the district to the southwest of the fault has tended fault can be determined at various points. The largest observed amount oc- to move northwestward with respect to the district across the fault. In- curs just northwest of its major bend, where, in and near Carrizo Plain, 100 terpretations of this innocent fact have been numerous and varied. The square miles of coarse, nonmarine upper Miocene sediments are now sur- present writer has not the slightest idea which of them is correct. Nor does rounded by finer-grained marine sediments of equivalent age, with there- there seem to be any clear and incontrovertible evidence as to the total fore, apparently no possible source. If these are moved by eye southeast- amount of this horizontal movement during the Tertiary period or any part ward [along the San Andreas fault] a distance of approximately 25 miles of it. The amount is probably more than 700 feet, the distance that can be they parallel the San Emigdio Mountains, seemingly the only possible measured in the offset of modern streams west of the Temblor Range. It source for them, indicating a total post-Miocene horizontal throw here may be 10 miles or 24 miles, or more, but the evidence for any of these along the rift of this amount. figures is inconclusive.

Among the geologists most familiar with different parts of the long course This statement indicates that Eaton was acquainted with Noble's of the fault, the notions held about its nature and history are very diverse. To some it is an ancient feature . . . To others it is a recent feature. At pres- strike-slip interpretation of the San Andreas and the 40 km of ent there is, on the whole, little more reason for holding one of these views right-slip provided an explanation for the juxtaposition of the than the other. marine upper Miocene strata in the Temblor Range with continen- tal beds of the same age immediately west of the San Andreas fault. Actually, all Reed had to say about the San Andreas fault in this Reed, in Geological formations and economic development of oil book is that he had reservations about accepting miles of strike-slip and gas fields of California (1943, p. 99-1 18), described and in- on the San Andreas. However, his Tertiary paleographic maps (see terpreted stratigraphic sections and showed four Tertiary his Fig. 31, p. 185) proved that he believed they were not sig- paleographic-isopachous maps without mentioning or indicating nificant. In this and other of Reed's writing, it is apparent that he strike-slip displacement on the San Andreas fault. This paper liked to explain the distribution of basement rock facies (Francis- clearly reveals that Reed did not subscribe to miles of horizontal can versus Sierran) and unlike stratigraphic sections by up-and- movement on the San Andreas fault or the need for palinspastic down movements on faults, or preferably by folding, with accom- maps to portray differences in early and late Tertiary paleogeo- panying erosion and deposition. graphic or paleogeologic maps. Reed and Hollister (1936), in their Structural evolution of South- Knowing that Reed and Eaton were friends and in direct com- ern California, wrote (p. 84): munication during parts of the 1930s and '40s, 1 wonder how the low-voiced and deliberate Ralph Reed and the high-voiced and ex- Another problem of great difficulty relates to the origin of the San Andreas citable Joe Eaton behaved when discussing movement on the San fault. During the Cretaceous the boundary [east side of Salinia] . . . may Andreas. have been mantled with sediments or perhaps Salinia remained above sea- level. On the later supposition, the San Andreas line, faulted or not, may Taliaferro, perhaps the strongest and most authoritative oppo- have been a shore line. nent to substantial strike-slip displacement on the San Andreas fault, wrote a long paper (1943) in which he claimed (p. 151 —161): In this book, the authors tried to explain the absence of Creta- ceous (and Franciscan) strata west of the San Andreas fault by up- Almost every assertion regarding the fundamental control of Coast Range lift and erosion down to the granitic basement of Salinia. They pre- structure has met with contradiction . . . The San Andreas fault is ancient ferred to do this mainly by folding but possibly by uplift on the and the horizontal movement is measurable in scores of miles; it is very young and the movement is measurable in thousands of feet. . . many of the fault. They apparently accepted strike-slip on the San Andreas as a current opinions regarding Coast Range structures are erroneous because late and not very significant mode of displacement. None of their they have confused the effects of two or more diastrophisms; this is particu- paleogeographic and isopachous maps were corrected for strike- larly true of the San Andreas. slip displacements. Along the ancestral Eocene San Andreas fault the movement was largely Taliaferro" (1938) presented a paper to The Cordilleran Section vertical, the downthrow being on the northeast. of the Geological Society of America entitled, "San Andreas fault in There is no evidence that the early Eocene fault along the northeastern ," in which he said (p. 254-255): margin of the Gabilan Mesa experienced any [more] movement, except where crossed by late Pliocene and Pleistocene faults, until the late Pleis- As a result of ten years mapping in the central Coast Ranges and three tocene when the present San Andreas fault was formed. summers spent along a 40-mile stretch of the San Andreas fault north of Although a major structural feature, the effects produced by all of the late Parkfield, certain conclusions contrary to the generally accepted views have Pleistocene and recent movements along it [the San Andreas) have not been been reached. comparable with those which resulted from the Plio-Pleistocene [and older] (1) It is very young [late Pleistocene). diatrophisms. (2) The total horizontal movement is small, certainly less than a mile. (3) It cuts across structural and topographic features developed in late The writer is well aware that the conclusions presented here will be contrary Pliocene and Pleistocene. to many of the current views . . . however, [they] are not based on hypothet- (4) It sends off no branches; faults which have been regarded as branches ical reasoning, or a preconceived idea, or on any of the conflicting state- are earlier features cut by the San Andreas fault. ments that have been made, but have developed gradually as field observa- (5) In many places it follows older faults, but in just as many places it is tions have accumulated during many years mapping over a wide belt from independent of such features and is not deflected by them. the Pacific Ocean to the San Joaquin Valley.

Apparently Taliaferro had not forgotten (or forgiven) Noble's It is obvious now that Taliaferro confused vertical separations on (1926) suggestion of 38 km of horizontal movement along the San faults with fault slip and, contrary to the last quotation above, his

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mapping, like that of most geologists, was influenced by his con- there were probably ancient periods of diasrrophism along the San Andreas cepts. Taliaferro argued, in this paper on the geology of the Coast line, the strike-slip movements may have had a relatively recent beginning. Ranges, that the horizontal shift on the San Andreas fault was less than one mile. According to gossip, he was reported to have said These quotations indicate that Wallace believed dip-slip dis- that the total strike-slip on the fault was probably no more than the placements on the San Andreas had been important, although good few feet which accompanied the 1906 earthquake. evidence for late strike-slip was presented. His cross sections show Wilson (1943), a student of Taliaferro, in his discussion of the up-and-down arrows, whereas now he would probably show the geology of the San Benito quadrangle, wrote (p. 250, 25 1, 252): symbols T (for toward) and A (for away) to indicate right-slip on the fault. Wallace was obviously reluctant to answer his own The San Andreas fault. . . extends in a northwest direction through the San questions about age of the fault, the total strike-slip, and the rela- Benito quadrangle . . . Recent movement along the fault has been chiefly tive importance of vertical and horizontal movements on the fault horizontal, the southwest side having moved relatively northwest. . . Hori- during Tertiary time, and along different segments of the San An- zontal displacement of about half a mile is shown by offset streams and ridges . . . Displacements of several tens of miles along the San Andreas dreas. It seems to me that he was unduly influenced by the opinions have been suggested in the past, but evidence against such large displace- of Reed (1933) and Taliaferro (1943), and perhaps by Noble's ap- ments have been presented by Reed 11933] and Taliaferro [19431 . . . The parent reneging (1933) on his 38 km of strike-slip (1926). Bear Valley fault marks the boundary between granitic basement |of Taliaferro (1951) contributed a long paper to the Cwologic Salinia] and Franciscan basement | northeast of the fault] ... Its course parallels and in part coincides with that of the San Andreas fault, which guich'book of the Sail hrancisco Hay C.ounties in which he described may explain the attribution of some of its characteristics to the San Andreas in considerable detail the stratigraphy and interpreted the geologic fault in the past . . . The Bear Valley fault differs in several important history of the entire region. His Plate 1 (opposite p. 128) comprises characteristics from the San Andreas fault . . . The Bear Valley fault shows eight rather detailed geologic sections crossing the Coast Ranges. an interesting succession of reversals of movement ... (1) The southwest He did not specifically describe the structural features of the region, side . . . was upthrown and Franciscan was eroded off the granite ... (2) Franciscan on the northeast side of the fault was thrust over granite on the but in the geologic history, he referred to the San Andreas fault as southwest side. Monterey sediments were eroded from the northeast side of follows: the fault ... (3) The most recent reversal of movement along the Bear Val- ley fault is a downthrow of the San Benito gravels (Plio-Pleistocene] on the One of the most important effects of this diastrophism [ referred to as a northeast side. Laramide pulsel was the formation of the ancestral San Andreas fault and the uplift of the Gabilan mesa. This mesa was upbowed in mid-Upper Cre- taceous . . . The vertical movement on the ancestral San Andreas fault must Wilson's Figure 6 (p. 227) shows three cross sections with arrows have been in excess of 15,000 feet in the central Coast Ranges . . . The pro- to indicate these reversals of dip-slip movement. Wilson followed found normal faulting in the lower Eocene left a strong imprint on all suc- others in assuming that Franciscan strata were deposited on granite ceeding events in the geologic in that it elevated a fairly broad block that runs diagonally through California from San Luis Obispo basement (a good illustration of the danger of what Chamberlin, in County northwestward to San Mateo County . . . western Marin County is his classic 1 897 paper, called the "ruling theory"). We now believe part of this block [Salinia). All the Mesozoic sediments were stripped from that the Bear Valley fault is a strand of the San Andreas zone, all of this block, exposing the ancient crystalline schists and plutonic rocks of the which are characterized by right-slip, and that the juxtaposition of basement complex, but the depressed regions on either side retained their thick prisms of pliable sediments [including Franciscan strata]. these unlike rocks can be explained by horizontal movement. Wallace (1949) mapped a strip some 32 km long that straddled the San Andreas fault and extended northwest from Palmdale. His Taliaferro did not discuss what he might have called the beautiful geologic map, in color and on the then new 1:24,000 top- "modern" San Andreas fault or refer to any horizontal (strike-slip) ographic map, connected with Noble's (1926) mapping to the movement on it. Obviously he stuck to the conclusions of his 1943 southeast. Wallace's stated queries were (p. 783): paper, which was that up-and-down (dip-slip) movements charac- terize the San Andreas. This interpretation, shared by many others, (1) Does the San Andreas rift date back to the early Tertiary or pre-Tertiary was based 011 the erroneous assumptions that Franciscan strata had time, or is the strike-slip an extremely recent feature cutting structural features formed by earlier displacement of different type? to lie on granitic basement, and that cross-fault stratigraphic mis- (2) Is the strike-slip of the rift many miles or less than a mile? matches had to be explained by vertical displacements. | Readers of (3) Does a different history of different portions of the rift account for the this paper of Taliaferro's might wonder, as I do, why he chose the discrepancy of interpretations? photograph, his Figure 7 (p. 150) reproduced from Plate 64B of the Commission's report (Lawson, 1908), showing the 1.5-m, left- He concluded (p. 799, 800): lateral offset of a fence. Could it be that he was trying to confuse others about the sense of slip on the San Andreas? Certainly, to me, The principal evidence of past strike-slip displacement along the San An- this offset is confusing.] dreas rift is the offset of stream channels . . . Little Rock Creek (Fig. 2), one of the best examples, shows a horizontal offset of over 1V2 miles . . . Verti- Crowell (1952) presented good evidence for miles of horizontal cal displacements are apparent from a study of the geomorphology. movement on the , which trends southeast through the western and may be a dead or dor- Based on the distribution of clasts in terrace gravels and their mant strand of the San Andreas zone. He maintained (p. 2030) that probable source terranes, he added (p. 801 -802): the present positions of two different masses of upper Miocene coarse con- It is hard to escape the implication that the north side of the rift has moved glomerate and sedimentary breccia, which crop out next to the San Gabriel 5 to 6 miles relatively eastward. . . . fault, apparently required a strike-slip displacement on the fault of many miles. Each mass contains coarse clasts of basement rock types which were washed into place from across the fault. At the present time, however, the And, regarding the age of the fault, he said (p. 803): regions across the fault from each deposit are mantled by sedimentary rocks older than the conglomerates, which means of course that basement rocks There are two important characteristics of the rift, the San Andreas line and of these areas were not available to erosion. But with a lateral displacement the San Andreas strike-slip displacement. In speaking of the antiquity of the of 15-25 miles, exposed source areas of appropriate composition are rift, careful distinction should be made between the two, because, although aligned properly with respect to the derived sediments . . . Although there

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are other great faults in California apparently similar to the San Gabriel, He then presented evidence for 1 82 m of right-lateral offset of a none of the others, including the San Andreas (Noble, 1926, p. 420; stream channel preceding the 1857 earthquake; offsets of some Taliaferro, 1943, p. 159) shows proof of great strike-slip movement. large stream channels of more than 1.6 km; ~8 km of slip since deposition of the late Pleistocene Harold Formation; a greater In summary, Noble (1926) started something important, which offset of the Pliocene Anaverde Formation; more than 48-km offset only a few others picked up, with arguments for miles of strike-slip of the Miocene ; and the unlike-basement- on the San Andreas, as well as on some other faults. However, most rock facies extending for more than 80 km along the fault, possibly geologists, apparently including Noble, dropped the idea in favor indicating earlier right-lateral movements beginning in early Ter- of minor and geologically late strike-slip resulting from a relatively tiary, or before, to provide a still greater amount of total cumula- new tectonic environment. In my opinion, they were unduly tive slip. influenced by such eminent geologists as Ralph Reed and N. L. Hewett (1954) in discussing faults in the region Taliaferro. All of them, including too many now, accepted fault said (p. 17): separations as seen in geologic sections as fault slips, thereby er- roneously assuming up-and-down movements. Generally speaking, The approximate dip Islip] displacement of many of the faults [northwest it seems that there was too little progress in understanding the na- trendingl is known to be several thousand feet; in only a few places is the ture and history of the San Andreas fault for too many years follow- existence of lateral movement inferred, and it is small compared with the ing the revelations accompanying the San Francisco earthquake. amount of dip movement. Along some of the faults that have been traced Perhaps the arguments for strike-slip were too weak to generate for distances of 10 miles or more, the blocks southwest of these faults seem to have dropped with respect to those on the northeast; a few miles away, productive controversy. however, the displacements commonly are reversed. These relations indi- cate a scissors pattern. HILL-DIBBLEE PROPOSAL TO 1965 These statements provide another example of taking fault sep- arations, as viewed in cross sections, to be indicative of fault slip; This era in the history of study of the San Andreas fault begins the so-called reversals of dip-slip or the implied scissors movements with the publication of evidence suggesting the possibility of hun- are descriptions of cross-fault geometry rather than of real relative dreds of miles of cumulative horizontal slip along the San Andreas movements (kinematics). Later mapping and analyses (for exam- fault (Hill and Dibblee, 1953), and ends after it was designated as a ples, see Dibblee, 1961; Garfunkel, 1974; Cummings, 1976) indi- transform fault separating lithospheric plates (Wilson, 1965). The cated that these faults in the Mojave Desert, which parallel the San Hill-Dibblee proposal was introduced in an oral presentation at the Andreas, are right-lateral slip faults, although little evidence for the 1952 meeting of Pacific Section, American Association of Petro- cumulative slip on them is available. leum Geologists. In essence, it said that regional geologic maps (mainly mapping and compilations by Dibblee) indicated cross- Allen (1957) reported on the San Andreas fault zone in San Gor- fault correlations that could be accounted for by strike-slip on the gonio Pass (p. 316, 346. 347): San Andreas; that the older the rock units, the greater the offset; The investigations here described were aimed at increasing the knowledge and that right-lateral slip has continued along the San Andreas fault of a part of the San Andreas fault system of California. The many tectonic from at least middle Cretaceous time to the present. The specific problems relating to this fault have been summarized by Hill and Dibblee's proposals of offset were: Pleistocene facies, 22 km; upper Miocene (1953) study . . . These investigations have stimulated further field work by strata, 104 km; lower Miocene, 280 km; Eocene, 360 km; Upper their suggestion that the total lateral displacement on the San Andreas fault Cretaceous, 5 1 2 km; and offset of basement rock facies, more than zone may be as much as 350 miles, in sharp contrast to a previous sugges- tion of less than 1 mile (Taliaferro, 1943) . . . The results of the present 560 km. study neither prove or disprove the existence of large lateral displacements These oral and published arguments for hundreds of kilometres along the San Andreas fault zone as a whole ... In view of the increasing of cumulative strike-slip on the San Andreas were shocking and evidence of complexity of strike-slip faulting within and south of the Trans- verse Ridges, . . . the writer feels that the entire zone between the Elsinore "taken with salt" at the time, but they did generate interest, con- fault and the eastern side of the Salton depression properly could be re- troversy, and additional field work. Like the San Francisco earth- garded as the San Andreas fault zone. No convincing evidence yet exists quake, this proposal revolutionized thinking about the fault. Sub- that any particular fault w.thin the 50-mile-wide zone deserves the parent sequently, some of these displacements have been proven to be too name . . . The mechanics of the Banning-San Andreas fault system suggest short, and others perhaps too long, but although more and better that reverse and thrust faulting [relatively raising the San Jacinto and San Bernardino Mountains) in the pass area have been caused by local control is still required, most geologists can agree, in the light of "deflection" of the San Andreas type of strain . . . Thus, local conversion of plate-tectonics theory, that the offsets proposed in 1953 are no strike-slip strain into vertical displacements along bounding faults of the longer incredible. San Gorgonio Pass is a reasonable explanation of both the pass and the un- Noble (1954), in his latest and most complete account of the usually high peaks adjacent to it. geology along the San Andreas fault (extending in a 67-km-long strip, northwestward from Cajon Pass) on the basis of his own Although Allen's work did not contribute to determinations of mapping over a period of some 40 years, came to the conclusion the amount of strike-slip on the San Andreas, his good mapping that there has been at least 48 km of strike-slip on the fault. He and reasonable analysis further emphasized a current problem; wrote (p. 44): where is the San Andreas fault, scnsu stricto, south of the Trans- verse Ranges? It should be noted, however, that the figure [.30 miles] given here applies Curtis and others (1958), dated and correlated granitic rocks in only to the San Andreas fault itself. If the speculation offered by Hill & the Sierra Nevada and Coast Ranges by the potassium-argon tech- Dibblee (1953, p. 453) that the San Gabriel and San Jacinto faults may be ancestral portions of the San Andreas fault can be proved correct, it is pos- nique, and they explained the position of Salinia in the Coast sible that the aggregate movement on these faults, could it ever be deter- Ranges as follows (p. 31): mined, would bring the estimates more nearly into accord [with the hun- dreds of miles of right-slip proposed by Hill & Dibblee in the Coast A displacement of at least 300 miles along the San Andreas fault appears to Ranges!. have occurred since Upper Cretaceous time.

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I believe this was the first correlation of Coast Range and Sierran geologic history can be inferred which explains the confusing stratigraphic basement rocks. However, the previous location of Salinia and anomalies [on opposite sides of the San Gabriel fault| that first led to the strike-slip hypotheses. exactly how it was related to the Sierran batholith are not yet known. They showed (Fig. 8, p. 1955) cross sections which resolved these King (1959) wrote in his classic volume, The evolution oj North anomalies by reversals of dip-slip movement on the San Gabriel America, (p. 169): fault. The accompanying paleogeographic maps show these up- and-down and scissor movements by plus and minus symbols. Total displacement on the San Andreas fault should be indicated by offset of basement rocks which have shared all its later movements. Matching of They concluded (p. 1953): basement rocks on the two sides is as yet inconclusive, but geologists work- ing in Southern California have found remarkable resemblances between When these cross-sections are combined with Figure 5, which is a section the basement of the San Gabriel Mountains southwest of it and those of the across the central part of the fault, they demonstrate fully the improbability Orocopa Mountains northeast of it, which lie near the Salton Sea 150 miles of any major horizontal movement on the Sail Gabriel fault. to the southeast. In my opinion, these writers did not fully appreciate the differ- This offset of Pelona schist from Orocopa schist, perhaps first ence between fault separation and slip, and they contrived an awk- suggested by Hill and Dibblee (1953, p. 450) and developed in ward succession of dip-slip events to explain cross-fault relations. considerable detail by Crowell (1962) and Ehlig and Ehlert (1972), These authors implied that the proposed miles of horizontal dis- has been contested by Woodford (1960) and Baird and others placement on the San Andreas fault could, like their interpretation (1974). of movements on the San Gabriel fault, be more easily and reason- King discussed (p. 169) the objections of Reed (1933) to Clark's ably satisfied by up-and-down (dip-slip) movements. (1930) fault-block hypothesis (referred to in the previous section of Bazely (1961) calculated 280 km of cumulative right-slip on the this history) and he tentatively accepted an alternate (strike-slip) San Andreas fault since early Miocene time by matching a sequence explanation for the juxtaposition of unlike stratigraphic sections. of marine, continental, and volcanic rocks in the San Juan Bautista Oakeshott (1959), in a comprehensive paper on the San Andreas area with a similar sequence in the San Emigdio Mountains on the fault in the , which accompanied several other (northeast) side of the fault. Bazely made this study as a grad- other papers on the San Francisco earthquake of 1957, wrote (p. uate student at the University of California, Los Angeles and con- 23): cluded that it confirmed one of the offsets suggested by Hill and Dibblee (1953). It may well be that a great ancestral San Andreas fault developed (with its Crowell (1962), in a comprehensive review entitled, Disjilace- largest displacement in early Eocene time) with thousands of feet of uplift of the western block to account for the removal by erosion of Franciscan and ment along the San Andreas fault, came to the following tentative Upper Cretaceous strata, leaving granite rocks exposed, while the eastern conclusions (p. 49-50): block was relatively downdropped, thus preserving rocks of these ages. Perhaps the apparent reversal of this vertical movement, which closed the 160-175 miles of right-slip on the San Andreas and closely associated Miocene epoch and caused the Monterey formation to be stripped from the faults since early Miocene is probable . . . Displacements greater than 160 eastern block, initiated a new regime in which displacement, in reality, be- miles referred to in the geological literature depend on evidence and argu- came right-lateral strike-slip. ments of a different order of acceptability . . . Cretaceous and Eocene strata exhibit possible separations of more than 320 and 220 miles, respectively, Here Oakeshott concurred with his professor (Taliaferro) that but the original distribution of these low dipping units . . . has not. . . been described. Older and greater displacements, up to as much as 400 miles de- there must have been an ancestral San Andreas on which pend on the supposed alignment ... of the boundary between Sierran "thousands of feet" of vertical displacement accounted for the ab- basement . . . and Franciscan rocks. . . . Much more work needs to be done sence, or presence, of parts of the stratigraphic section on one side to make these [greater] proposed correlations acceptable. of the fault. On the other hand, Hall (1960) used paleo-isotherms as indi- The words of caution expressed here are still applicable. cated by upper Miocene molluscan assemblages in the Coast Bailey and others (1964) came up with several innovative ideas in Ranges, to conclude that post-Miocene offset on the San Andreas their analysis of the distribution and fades of the Franciscan As- fault was between 80 and 240 km (p. 281): semblage in California and their stratigraphic and structural rela- tions to adjoining rocks. They discussed possible roles of the San By plotting the present positions of the late Miocene paleo-molluscan prov- Andreas fault and movement along it and possible explanations for inces and isotherms |based on these assemblages], provincial and tempera- the emplacement of the Salinian corridor of granitic basement be- ture differences are revealed on opposite sides of the San Andreas fault. tween areas of Franciscan rocks. They argued for a tectonic Right-lateral slip displacement of latitudinal provincial boundaries is ap- proximately 120 miles. mechanism of oblique rifting, initially along a Mesozoic San An- dreas fault, something like the present rifting of from the east side of the to effect perhaps as Perhaps the most immediate controversy about miles of strike- many as 240 km of right-lateral shift; this could provide for both slip developed concerning the San Gabriel fault. Crowell's (1952) the position of Salinia and a reasonable strike-slip on the San An- 19-40 km of right-slip was contested by several southern California dreas fault. They also proposed the existence of a regional Coast geologists, culminating in a paper by Paschall and Off (1961). They Range Thrust, locally exposed, to explain their Cretaceous Great wrote (p. 1941, 1956): Valley marine section of granitic derivation on coeval Franciscan rocks that presumably rest on oceanic basalt. Their conclusion (p. The purpose of this paper is to examine the San Gabriel fault, a possible branch of the San Andreas, ... to determine whether large horizontal 8) is as follows: movement has occurred . . . Strike-slip faulting of the order of tens to even hundreds of miles has been suggested for various faults in California. At Several mechanisms that might account for the major dislocations are large present, however, there appears to be an excellent case to be made in many strike-slip movement, rifting and westward drifting of the entire Coast instances for dominantly vertical movement ... By using dip-slip alone, a Ranges, and thrust faulting or gravity sliding. However, none of the

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mechanisms discussed will alone completely explain the data now available, The lateral offset indicated by correlation of the southern Temblor Ranges although some combination of these dislocations may provide a satisfactory with Pinnacles area is approximately 160 miles since late Miocene time. solution. This is considerably greater than the 65 miles suggested by Hill and Dibblee (1953) but is consistent with the work of Bazely (personal communication) and others on the lower Miocene. Turning again to Oakeshott (1964), in a paper entitled, The San Andreas fault revisited, I find the following (p. 268): A highly successful conference on geologic problems of the San For a distance of 350 miles north of the San Emigdio Mountains the San Andreas fault was held at Stanford University in September of 1967 Andreas fault zone appears to separate late Mesozoic ensimatic eugeosyn- which resulted in the 375-page "Proceedings." The second part of clinal Franciscan rocks from the late Mesozoic sialic granitic rocks [of this four-part, three-day program was captioned "Offsets in Time." Salinia to the westj. Distribution of these two great rock units can not be Dickinson and Grantz (1968), the organizers of the Conference and readily explained by strike-slip movement (on the San Andreas fault) but does appear to require vertical displacements on the order of more than 10 editors of the Proceedings, presented a graph (p. 118), indicating miles. cumulative right-slip on the fault since the Cretaceous. Half of the dozen or so points which establish their curve are from papers pre- I do not agree here with my respected friend Gordon Oakeshott, sented at the conference. The Hill-Dibblee (1953) offsets, also but I admit that my "ready" solution of ~720 km of right-slip plotted on the graph, are compatible and, therefore, are generally along the east side of Salinia (Hill, 1971) has not been widely ac- confirmed by the newer data. One of the conference papers cepted. (Addicott, 1968, p. 144-165), written on the basis of cross-fault In another paper, Oakeshott (1965) contended (p. 5): correlations of lithofacies, isopachs, and fossil assemblages, indi- cated right-lateral displacements of 320, 272, 208, and 128 km of In central and , matching of stratigraphy, structure and Oligocene, early Miocene, middle Miocene, and late Miocene geologic history across the San Andreas fault, from Late Cretaceous to strata, respectively. Pleistocene time, leaves little room for large strike-slip displacement. . . The San Andreas zone, during Cenozoic time, was a locus of deposition of sedi- The last quotation in this section of this history is from Wagner's ments; this has made measurement of lateral offsets uncertain. Character of (1969) abstract of a paper presented at the Geological Society of sediments, however, offers convincing evidence of large, adjacent vertical America Cordilleran Section meetings. He wrote (p. 71): uplift ... I have been concerned about these problems [of lateral versus vertical displacements], and have made field checks along the San Andreas middle Miocene strata of the Caliente Formation ... on the western side of fault from one end to the other to try to resolve them . . . Critical objective the fault [San AndreasJ were deposited under nonmarine conditions; they re-evaluation of geologic mapping and the literature, and years of spot- thicken and coarsen to the east, indicating a source in that direction. Middle checking important segments of the fault in the field, favor predominantly Miocene strata of the Monterey Formation east of the fault, however, were vertical movement rather than large strike-slip displacement on the San An- deposited in a bathyal marine environment. About 100 miles of recon- dreas fault in pre-Quaternary time. structed [left-lateralj movement brings a terrestrial source area, as well as a similar marine sequence, into palinspastic position.

Oakeshott (1966), in still another of his several papers express- This is confirmation of large horizontal offset on the San Andreas ing skepticism about miles of strike-slip on the San Andreas, argued fault to separate rock facies of the southern San Joaquin Valley- (p. 371): Temblor Range area, east of the fault, from rocks of the same age but of different facies in the Caliente Range- area, Late Cretaceous and Tertiary stratigraphy, structure and geologic history west of the fault, earlier proposed by Eaton (1939) and several which can be matched across the fault in central and northern California others. leave little room for strike-slip displacement of more than a mile or two . . . Distribution of late Mesozoic Franciscan rocks and granitic rocks of near- It should be noticed that the last quotation is from a 1969 paper, equivalent age cannot be satisfactorily explained by large strike-slip move- whereas the next section begins with a 1965 one. Obviously, this is ment, but does appear to require vertical displacements in the order of more because the work to establish and refine measurements of cumula- than 10 miles. tive offset on the San Andreas fault since specific geologic times continues beyond any arbitrary date. There is additional time over- These quotations all indicate that Oakeshott, at least until 1966, lap also because the concepts of plate tectonics (for example, Vine preferred dip-slip movements on the San Andreas fault. and Matthews, 1963) led to the 1965 involvement of the San An- Some other quotations bearing on the sense and cumulative dreas. movement on the San Andreas, which illustrate differences of opin- The era 1953-1965 can be considered as a time of recognition, ion, are as follows: Hamilton and Myers (1966) in their Cenozoic testing, and finally a general acceptance of at least tens and proba- tectonics of the western United States stated (p. 511): bly hundreds of kilometres of cumulative slip on the San Andreas fault. It was a time of considerable controversy, and the final an- We regard it as proved — many others do not — that the San Andreas and swers on time of initiation, cumulative slip, and rates of movement related faults of have an aggregate Cenozoic displace- ment of hundreds of kilometers. on the fault are still not in. However, with the introduction of plate-tectonics theories, firmly established by many articles in Baldwin (1967) in the and adjacent San Andreas geological and geophysical publications since 1967 (for example, fault guidebook said (p. 92): Heirtzler and others, 1968), kilometres of strike-slip on faults is no longer a contentious concept. It should be noted that these maps lisopachousj straddle the San Andreas fault but that no isopach interruption or offset is shown across the fault trace. Marked similarities of facies and thickness occur from Eocene into WILSON'S PROPOSAL AND SEQUEL middle Miocene time. Wilson (1965) proposed a new class of faults, called "transform Fletcher (1967), in the same publication, concluded that the faults," as one kind of boundary between lithospheric plates. It post-late Miocene cumulative right-slip on the San Andreas in cen- seems that he developed this revolutionary new concept while tral California is —256 km (p. 68): working with geologists and geophysicists at Cambridge Univer-

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sity, including, among others, Vine and Matthews (1963), who are After publication of the Earthquake Investigation Commission given credit for an early idea of plate tectonics. Wilson used the San volumes (Lawson, 1908; Reid, 1910), very little mapping and few Andreas fault as one type, the ridge-ridge transform, characterized new interpretations of the fault were forthcoming, presumably be- by the sense of slip being opposite to the offset of the oceanic cause the geological community was satisfied with the completeness spreading ridge. This characteristic of ridge-ridge transforms was of those publications. However, there was additional mapping, confirmed by seismic first motion solutions (Sykes, 1967). Sub- especially by the U.S. Geological Survey, as topographic maps of sequently, many papers, especially in the 1968 volume of the Jour- the southern Coast Ranges became available. This mapping, to aid nal of Geophysical Research, have provided data and interpreta- and encourage oil exploration, added to structural and strati- tions about transform faults (for example, McKenzie and Parker, graphic information along the San Andreas fault. Generally, these 1967; Morgan, 1968; Johnson, 1967; van Andel, 1969; Garfunkel, data were interpreted as indicative of earlier up-and-down (dip- 1972; Freund, 1974; Hill, 1974a). (Note: 1 was in the audience at slip) movement on the fault. the 1964 American Association of Petroleum Geologists meeting in In an important, but ignored, paper in the context of this history, Toronto, Canada, when Wilson discussed and demonstrated trans- Vickery (1925) suggested several kilometres of strike-slip on the form faults with a cardboard model. I was aroused to take the floor Sunol (Calaveras) fault. No other proposal for miles of horizontal to warn the audience not to accept a new name for strike-slip faults. movement along any other fault associated with the San Andreas 1 here apologize to Wilson for not appreciating at that time a sig- was made until Noble (1926) suggested the possibility of 38 km of nificant difference between his oceanic faults and conventional cumulative offset on the fault in southern California. This proposal strike-slip faults. And, in spite of my question about the San An- generated considerable interest and controversy. However, most dreas as a transform fault (Hill, 1974b), I am now inclined to be- geologists, apparently including Noble (1933), were persuaded by lieve that it participates in a complex diffused boundary between respected geologists and their publications (for example, Reed, the North American and Pacific lithospheric plates, and shares at 1933; Taliaferro, 1943) that slip of such magnitude was unreason- least some of the characteristics of oceanic transform faults.) able. Although the San Andreas fault has been generally accepted as a Twenty-seven years later, Hill and Dibblee (1953) presented evi- transform fault, separating a segment of the boundary between the dence, based on geologic relations along a nearly 480 km stretch of North American and Pacific plates, some objections have been the fault zone in the southern Coast Ranges, for perhaps more than raised (Hill, 1974b, Woodford and Mclntyre, 1976). However, it 560 km of cumulative right-lateral slip. Their cross-fault strati- appears that the San Andreas must play some role in separating graphic correlations indicated 22, 104, 280, 360, 512, and 560+ these plates that theory, movements of adjacent oceanic crust, and km of slip since Pleistocene, late Miocene, Miocene-Oligocene, strain analyses of continental geology have only crudely resolved. Eocene, Late Cretaceous, and mid-Cretaceous time, respectively. Many references to the San Andreas fault continue to appear in Surprisingly, there was little published opposition to their tentative the current literature, especially about its role in plate tectonics (for conclusions, but much interest was aroused, and many geologists examples, those by Atwater, 1970; and Dickinson and Snyder, were stimulated to discover facts which might confirm, condemn, 1979). In addition, geodetic and geophysical studies and detailed or modify these cross-fault correlations. Although arguments mapping of surface features and sedimentary facies along against these suggestions were mustered, the consensus of the the San Andreas have been accomplished, especially by the U.S. geologic community, especially as indicated by the Stanford Uni- Geological Survey in connection with an ongoing seismic hazard- versity conference of 1967 (Dickinson and Grantz, 1968), tended reduction program (as one example, see Vedder and Wallace, 1970, to confirm, with modifications, these displacements. Finally, with on recent breaks along the San Andreas fault between Cholame the introduction and acceptance of plate-tectonics theories, and Valley and Tejon Pass). However, the many post-1965 studies are especially with Wilson's (1965) proposal that the San Andreas is a probably too recent to be properly appraised in a historical context. transform fault between the North American and Pacific plates, Therefore, this seems to be an appropriate place and time to end there is no longer any influential objection to substantial strike-slip this history. along the San Andreas fault. This history of understanding the San Andreas fault is high- SUMMARY lighted by a few revelations which resulted in conceptual revo- lutions. Obviously, the first revelation was the 320-km zone of This history of the recognition, mapping, and interpretations of ground rupture accompanying the 1906 San Francisco earthquake; the San Andreas fault began with accounts of pre-1906 mapping of this led to the recognition of strike-slip faulting and the elastic- isolated segments of the fault. Then, on April 18, 1906, some of rebound theory of earthquakes. Noble's (1926) suggestion of 38 these segments were connected by ground breakage, and the zone km of right-slip constituted a new interpretation, partially aborted, was later extended by following geomorphic features indicative of that was reintroduced and augmented by Hill and Dibblee (1953). earlier fault displacements. The continuous zone of ground distur- Finally, plate tectonics and Wilson's (1965) introduction of the bance that was revealed by the San Francisco earthquake proved transform fault gave the first, although partial, explanation for the existence of a several-hundred-mile-long crustal fracture now strike-slip displacements of hundreds of miles. known world-wide as the San Andreas fault. Horizontal movement (strike-slip) was evidenced by offsets of as much as 4.7 m of man- CONCLUSIONS made (fences) and natural linear (stream channels) elements. This sense of movement along a major fault was apparently first recog- We can speculate, as an "after-the-facts" exercise, how this his- nized then, and the San Andreas became famous as a long, active tory would have been modified if geologists had been working in structure, capable of generating great earthquakes. In addition to southern California when the 1857 Fort Tejon earthquake oc- establishing lateral displacement as an important mode of fault slip, curred. Surely strike-slip movement would have been recognized, a dynamical analysis produced the elastic rebound theory of earth- the long and zone would have been traced for several quakes. hundred miles, the elastic-rebound theory might have been formu-

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lated (certainly, if a G. K. Gilbert had been there), and the fault ACKNOWLEDGMENTS would have some other name. However, it is also likely that some of the intrenched, but erroneous, concepts of that time would have I am most thankful for the use of the Woodford Library, and am acted to retard progress in understanding the nature and history of greatly indebted to Professors A. O. Woodford, A. K. Baird, and displacement on this great fault. After the 1906 San Francisco D. H. Zenger, Science Librarian Brian Ebersole and Secretary Jean event, the principal conceptual fallacies, or "ruling theories" MacKay, of Pomona College, for aid in the preparation of this ac- (Chaniberlin, 1897) which retarded progress in understanding the count. I also appreciate the encouragement and help of Professors San Andreas were (1) resistance to accepting strike-slip as a com- W. B. Wadsworth and Dallas Rhodes, and Lisa Rossbacher, of mon mode of fault displacement; (2) the assumption, without evi- Whittier College. dence, that Franciscan strata were deposited on granitic basement; (3) the assumption that offset topographic surfaces and strati- APPENDIX 1. BIOGRAPHICAL SKETCHES graphic sections across the fault resulted from up-and-down (dip- slip) movements; and (4) the reluctance to accept the possibility of John C. Branner (1850-1922), Ph.D., University of Indiana, many miles of horizontal offset on the fault. Confusion between the 1885; became a geology professor at Stanford University in 1892; geometry and kinematics of faulting, common even today, seems to and the second president of that institution in 1913. He had a good have been the single most important conceptual error involved in reputation as a geologist and teacher. He was the principal author holding back progress in understanding the San Andreas fault. On of the U.S. Geological Survey Santa Cruz Folio 163. The Branner the other hand, understanding of the San Andreas has been accel- Club, a geological society in Southern California, is named in his erated by (1) the San Francisco earthquake, (2) detailed geologic honor. He was a member of the Earthquake Investigation Com- maps of the southern Coast ranges, (3) the availability of aerial- mission, but it seems that he and Lawson were not very compatible. photo maps, (4) new concepts about strike-slip faults and the Bruce L. Clark (1880-1945), Ph.D., University of California, paradigm of plate tectonics, and (5) intensified studies motivated by 1913; Professor, University of California 191 1-1945. He was a controversies. Of these, the San Francisco earthquake was probably successful professor and competent paleontologist, specializing in the most important factor in accelerating knowledge about the San lower Tertiary marine megafossils. His stratigraphic studies lead to Andreas fault. tectonic interpretations, but with limited background in structural We can also speculate, as an exercise in prediction, how concepts geology, he attracted controversy — for example, with petroleum about the San Andreas will change, as they surely will, in the future. geologist Ralph Reed and Professor . The latter We are undoubtedly basing some of our current concepts on in- apparently took delight in publicly criticizing Clark's geologic in- adequate facts, fallacious assumptions, and conceptual errors terpretations. which will, when exposed, change at least some of the appendages Harold W. Fairbanks (1860—1952) was graduated from the of our "elephant," or perhaps even a major part of the "body." The University of Michigan in 1 890, became an assistant geologist with history of science and the history recorded here tend to predict that the California State Mining Bureau, received his Ph.D. in 1896 through unforeseen and revolutionary new concepts our present in- from the University of California, and became a geologist with the terpretations of the San Andreas fault will, in time, become obso- U.S. Geological Survey. He wrote more than 50 geologic reports lete. There are surely more questions about the San Andreas fault (including the U.S. Geo.ogical Survey San Luis Obispo Folio 101). and its role in regional and global tectonics now than at any time in He undoubtedly saw more Coast Range geology than any of his the past (contrary to Jordan's 1907 statement that the Earthquake contemporaries (a proto-type of Tom Dibblee). He left geology Commission report would contain all the answers). Problems such about 1915, possibly because of disagreements with Lawson, to be- as (1) Where are the ends of the fault? (2) Why does it have several come a geography teacher in the Los Angeles School system. prominent "bends"? (3) When and where did it originate, and was Grove Karl Gilbert (1843-1918) of the U.S. Geological Survey there a proto-San Andreas? (4) Where and when will it generate was stationed in Berkeley at the time of the earthquake and, as a the next great earthquake? (5) How does the San Andreas relate to member of the Earthquake Commission, contributed substantially the rotated and translated mini-blocks in southern California as to field and theoretical studies of the San Andreas fault and the indicated by paleomagnetic studies (Kamerling and Luyendyk, earthquake. A classic biography by Davis (1927), an analysis of his 1979)? There are many more current questions and problems, and philosophy of science by Gilully (1963), and a memorial by Men- more which will be posed as new data and new interpretations are denhall (1919) help to explain why Gilbert had such a good repu- developed. tation as a geologist. As recorded here, he understood the difference History is a more-or-less objective account of what man has between fault separation and fault slip (1908); he was probably the done. In this history of understanding the San Andreas fault, 1 have first to explain the origin of earthquakes by elastic rebound (1906); been both historian and geologist. Thus, 1 have tried, although in- and he knew about as much about earthquake prediction (1909) as completely and subjectively, to provide by quotations from original is known today. Gilbert contributed greatly to the fields of sources and accompanying comments, both conventional history geomorphology, glaciology, igneous activity, paleontology, and geologic history. These histories will continue to change, but meteorology, seismology, basin-and-range structure, isostasy, and too slowly if we accept the present simplistic interpretations of the the philosophy of science. He began geology as an assistant in role of the San Andreas fault in plate tectonics, as is already in- Ward's Cosmos Hall in 1867; he worked on the Wheeler and trenched in textbooks. A continued effort is required in order to Powell surveys and with the U.S. Geological Survey from 1879- produce pertinent new data and fruitful new interpretations. If we 1918. He was the president of at least seven important scientific remain dissatisfied with present knowledge, we can count on both societies, and was twice president of the Geological Society of progress in our understanding of the San Andreas and a continua- America and the Geological Society of Washington, D.C. Gilbert's tion of the progressive history of that understanding. Let us keep good geology was also recognized by numerous medals and other both of these histories rolling along. awards. After being gone for more than 60 years, Gilbert is still in

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rhe "limelight" as evidenced by a well-attended Geological Society Arnold, R., and Johnson, H., 1910, Geology and oil possibilities of the of America symposium in 1979 and the forthcoming GSA Special Midway-Sunset area: U.S. Geological Survey Bulletin 406. Atwater, T., 1970, Implications of plate tectonics for the Cenozoic tectonics Paper 183 on the scientific ideas of G. K. Gilbert. of western North America: Geological Society of America Bulletin, Andrew C. Lawson (1861-1952), Ph.D., Johns Hopkins, 1888; v. 81, p. 3513-3536. Canadian Geological Survey, 1883-1890; Professor at the Uni- Bailey, E. H., and others, 1964, Franciscan and related rocks, and their sig- versity of California, 1890-1928, and Emeritus Professor, 1928- nificance in the geology of western California: California Division of Mines and Geology Bulletin 183, 177 p. 1952. Vaughan (1970) has written a captivating biography of this Baird, A. K., and others, 1974, Transverse Ranges province — A unique fabulous but controversial, highly productive geologist and suc- structural-petrochemical belt across the San Andreas fault system: cessful teacher. According to Vaughan (p. 266), the first geological Geological Society of America Bulletin, v. 85, p. 163-174. field course for university credit was organized and taught by Law- Baldwin, T. A., 1967, Morphologic clues to geologic history of northern son. Lawson is reported (p. 60) to have enabled his field class at Salinas Valley and San Andreas fault, in American Association of Pe- troleum Geologists Pacific Section Guidebook — Gabilan Range and Carmelo (Carmel) Bay to appreciate the difference between re- adjacent San Andreas fault, p. 92-94. corded geology and the geologic record, since they, including Law- Bazely, W.J.M., 1961, 175 miles of lateral movement along the San An- son, had read about granite intruding Miocene strata there, but in- dreas fault since lower Miocene? [abs.|: Pacific Petroleum Geology, v. stead they saw these strata resting upon an eroded surface of gra- 15, no. 5, p. 2—3. nite. (I suffered through one of Lawson's seminars and to me he Branner, J. C., 1906, An authoritative opinion: Mining and Scientific Press, v. 92, p. 347. seemed to be opinionated and intolerant, but a highly competitive 1907, Geology and the earthquake, in Jordan, D. S., ed., The Califor- and competent geologist.) nia earthquake of 1906, p. 63—77. Levi F. Noble (1882-1965), Ph.D., Yale University, 1909; U.S. Branner, J. C., and others, 1909, Santa Cruz, California, Folio 163: Geological Survey, 1909-1965. In 1910, he settled on a wedding- Geologic atlas of the United States, U.S. Geological Survey. Campbell, M. R., 1902, Reconnaissance of the borax deposits of Death Val- present ranch in Valyermo, California. His principal geologic ley and the Mohave Desert: U.S. Geological Survey Bulletin 200, 23 p. studies were in the Death Valley region and on the San Andreas Chamberlin, T. C., 1897, The method of multiple working hypotheses: fault, which traversed his ranch. Journal of Geology, v. 5, p. 837-850 and reprinted in 1931, Journal of Geology, v. 39, p. 155-165. Ralph D. Reed (1889-1940), Ph.D., Stanford University, 1924; Clark, B. L., 1929, Tectonics of the Valle Grande of California: American became a distinguished petroleum geologist, and wrote Geology of Association of Petroleum Geologists Bulletin, v. 13, p. 199-238. California (1933) and with J. S. Hollister, Structural evolution of 1930, Tectonics of the Coast Ranges of middle California: Geological southern California (1936). Society of America Bulletin, v. 41, p. 747-828. Steven Tabor (1882-1962) received his A.B. from Stanford in 1935, Tectonics of Mount Diablo and Coalinga area(s), middle Coast Ranges of California: Geological Society of America Bulletin, v. 46, 1906 and Ph.D. from the University of Virginia in 1912. He was p. 1025-1078. professor of geology at the University of South Carolina from Crowell, J. C., 1952, Probable large lateral displacement on the San Gabriel 1912. Tabor assisted Branner in field studies connected with the fault, southern California: American Association of Petroleum San Francisco earthquake, wrote a report (1920) on the Inglewood Geologists Bulletin 36, p. 2026-2035. earthquake in southern California, and was considered to be an au- 1962, Displacement along the San Andreas fault, California: Geologi- cal Society of America Special Paper 71,61 p. thority on seismology. It seems that both Branner and Tabor fa- Cummings, D., 1976, Theory of plasticity applied to faulting, Mojave Des- vored the name "Portola-Tomales" for the fault, but as usual, Law- ert, southern California: Geological Society of America Bulletin, v. 87, son won the argument with his choice for a name, "San Andreas." p. 720-724. Nicholas L. Taliaferro (1890-1961), Ph.D., University of Curray, J. R., and Nason, R. D., 1967, The San Andreas fault north of Point Arena, California: Geological Society of America Bulletin, v. 78, California, 1920; petroleum geologist, 1914-1926; professor, p. 413-418. University of California, 1926-1961. He was a field-oriented Curtis, G. H., and others, 1958, Age determination of some granitic rocks "geologist's geologist" who strongly opposed evidence for miles of in California by the potassium-argon method: California Division of strike-slip on the San Andreas and, therefore, influenced his many Mines Special Report 54, 16 p. students, and others, to promote his prejudices. Davis, W. M., 1927, Biographical Memoir Grove Karl Gilbert (1843- 1918): National Academy of Science, 5th Memoir, v. 21, 303 p. Frederick P. Vickery (1880-1965) was born in San Rafael, Dibblee, T. W., Jr., 1961, Evidence of strike-slip movement on northwest- California, very close to the San Andreas fault. His B.S. degree trending faults in the western Mojave Desert, California: U.S. Geolog- came from the University of California in 1905, and Ph.D. from ical Survey Professional Paper 424-B, p. B197-B199. Stanford in 1925. He taught geology at the University of Califor- Dickinson, W. R., and Grantz, A., 1968, Indicated cumulative offsets along the San Andreas fault in the , in Dickinson, nia, Los Angeles, from 1922-1926; worked for the Miley and W. R., and Grantz, A., eds., Proceedings of conference oil geologic Western Gulf Oil companies from 1926-1932; and taught at Sac- problems of the San Andreas fault system: Stanford University Publi- ramento Junior College from 1932. cations, Geological Science, v. 1 1, p. 1 17-120. Dickinson, W. R., and Snyder, W. S., 1979, Geometry of subducted slabs REFERENCES CITED related to San Andreas transform: Journal of Geology, v. 87, p. 609- 627. Addicott, W. O., 1968, Mid-Tertiary zoogeographic and paleogeographic Eaton, J. E., 1939, Geology and oil possibilities of Caliente Range, Cuyama discontinuities across the San Andreas fault, California, in Dickinson, Valley and Carrizo Plain, California: California Journal of Mines and W. 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