AN ABSTRACT OF THE THESIS OF LEONARD TIMOTHY STITT for the degree of MASTER OF SCIENCE GEOLOGY presented on June 5, 1980 Title: GEOLOGY OF THE VENTURA AND SOLEDADBASINS IN THE VICINITY OF CASTAI LOS ANGELES COUNTY, CALIFORNIA - Abstract approved: Signature redacted for privacy. 'Dr. RoberIV. Yeats Surface and subsurface mapping are combined to determine the geologic history along the San Gabriel fault near the town of Castaic. Palomas Gneiss, Whitaker Granodiorite, and Pelona Schist are base- ment terranes encountered in the subsurface. West of the San Gabriel fault, basement is unconlormably overlain by marine middle to late Miocene Modelo Formation.The late Miocene to early Plio- cene Towsley Formation overlies the Modelo and wasdeposited in a submarine fan environment.East of the San Gabriel fault, marine Paleocene San Francisquito Formation accumulated while Pelona Schist was undergoing regional metamorphism at depths of 20 to 27 kilometers. Nonmarine Oligocene (?) Vasquez Formation is faulted against both the Pelona Schist and San Francisquito Formation. Charlie Canyon Megabreccia accumulated in late Oligocene (?) time as a large landslide deposit.The source is controversial, but may have beenirorn the LaPanza Range. PelonaSchistbearingSan Francis- quito Canyon Breccia accumulated in late Mi.ocene('?) (Bar stovian) tune as the Pelona Schist first became subject to erosionin northern Soledad basin.Nonmarine alluvial fan and lacustrine depositsof the middle to late Miocene Mint Canyon Formationunconforrnably overlie older units east of the San Gabriel fault and apparentlyintertongue with San Francisquito Canyon BrecciaA late Miocene (Monnian) marine transgression resulted in depositionof the Castaic Forma- tion in Soledad basin while the Modelo and possiblyTowsley Forma- tions accumulated in Ventura basin.Violin Breccia intertongueS with Castaic Formation and accumulated at the base of a MioceneSan Gabriel fault scarpMarine Pliocene Pico Formation unconforniably overlies the Castaic Formation east of the SanGabriel fault and con- formably overlies the Towsley Formation west of theSan Gabriel fault; it is overlain conformably by marine tononniarine Plio- Pleistocene Saugus Formation.Quaternary landslides, and older, intermediate, and younger alluvium overlie older rocksthroughout the stud.y area. The St. Francis fault may have been active in lateOligocene and early Miocene time, removing Charlie Canyon Megabrecciaby right-slip from a possible source in the La Panza Range.The low- angle San Francisquito fault and associated Bee Canyonfault and San Francisquito syncline were active after depositionof the Charlie Canyon Megabreccia but prior to deposition of the Mint Canyon FormationThe San Gabriel fault became active after deposition of the Mint Canyon Formation in late Miocene timeThe San Gabriel fault exhibits right-lateral separation of approximately 60 kilometers on the Mint Canyon and older formations, approximately 30 kilometers on Violin Breccia and Modelo Formation, and about two kilometers on the Pico FormationSan Gabriel fault "CIi ('p) and Castaic Hills reverse fault moved in late Miocene time and became inactive prior to deposition of the Pico Formation.The Charlie Canyon antidli.ae, Charlie Canyon syncline, Castaic anticLine, and Ridge Basin syncli.ne were formed in the Castaic Formation prior to deposition of the Saugus FormationThe Saugus is deformed by(1) folding which produced the Dry Canyon syncline, Dry Canyon anticline, Townsend syncixie, Lonia Verde anticline, North and South Hasley Canyon synclines, and Oak Canyon antacline, (2) reverse faulting on the south-dipping Hasley fault; (3) normal faulting in eastern Castaic Hills oil field; (4) normal faulting on the San Gabriel fault.The San Gabriel fault may also offset Quaternary aUuvium by normal separation in Castaic Creek. Geomorphic evidence suggests continuing movement on the San Gabriel fault, but the nature of seismic activity on the fault is still unresolved. Geology of the Ventura andSoledad Basins in the Vicinity of Castaic, Los Angeles County, California by Leonard Timothy Stitt A THESIS submitted to Oregon State University in partial fuLfillment of the requirements for the degree of Master of Science Completed June 5, 1980 Commencement June 1981 APPROVED: Professor of Geology and Eology Department Chairman in charge of major Dean of Graduate School Date thesis is presented June 5, 1980 Typed by Opal Grossnicklaus for Leonard Timothy Stitt ACKNOWLEDGEMENTS I would like to thank Kees A. De Jongof theUniversity of Cincinnati for encouraging my interest in structuralgeology, and Robert SYeats of Oregon State University for introducing me tothe San Gabriel fault problem and advising me during the courseof the thesis.Professors Keith F. Oles and J. Granville Johnson ofthe Department of Geology and Assistant Professor Stephen H.Johnson of the School of Oceanography, Oregon State University,served on the thesis committee. John C. Crowell of the University of California, SantaBarbara provided access to his unpublished maps, and discussionswith him were useful in guiding the course of thestudy.Alex Romero of Castaic provided access to the study area and a base camp duringthe field season.Jane Robles of the California Division of Oil and Gas in Santa Paula, and Jack Tucker of the California WellSample Repository in Bakersfield provided assistance in obtainingsubsurface data.William B. Wadsworth of Whittier College assisted in obtaining aerial photos of the study area from the Fairchild Collection. I would like to thank fellow graduate students Frederick M. Nelligan, Jill T. Schlaefer, Ibrahim A. Cemen, Kermit E. Shields, and Kevin J. Lant of Ohio University, and James P. Olson, JamesW. McDougall, Mary Clare Jakes, Patrick A. Jackson, and David W. Hanson of Oregon State for their friendship.Jeff Lane of Oregon State helped construct some of the cross sectionsDrafting was done by Paula L Pitts, Christopher Rademaker, and EdwinR Howes.The final manuscript was typed by Opal Orossnicklaus. Special thanks go to my wife Diane for her patient support and love. This project was funded under U. S. Geological Survey grant 14-08-0001-16747 of the Earthquake Hazards Reduction Program Atlantic Richfield Company provided support for field work during the summer of 1978. TABLE OF CONTENTS INTRODUCTION Regional Setting Purpose and Scope of Study 4 Methods of Study 5 Geographic Sketch 6 Previous Work 8 S TRA TIGRAPHY 12 General Statement 12 Basement Complex 17 San Francisquito Formation 24 Vasquez Formation 25 Charlie Canyon Megabreccia 28 San Francisqu.ito Canyon Breccia 30 Mint Canyon Formation 33 Castaic Formation 37 Violin Breccia 43 Rincon Formation 44 Modelo Formation 45 Towsley Formation 48 Pico Formation 52 Saugus Formation 54 Pacoirna Formation(?) of Weber (1979) 58 Olde r Alluvium 59 Intermediate- age Alluvium 59 Younger Alluvium 60 Landslides 60 STRUCTURE 61 General Statement 61 Stage I Structures 66 Eastern Part of the San Fraricisquito Syncline 66 Bee Canyon Fault 66 Dry Gulch Fault 66 Community Fault 67 San Francisquito Fault 67 St. Francis Fault Zone of Smith (1977) 69 Canton Fault 69 Stage II Structures 70 Western Fart of the San Francisquito Synchne 70 Charlie Canyon Anticline, Charlie Canyon Syncline, and Castaic Antic line 70 Ridge Basin Syncline 71 Normal Faults East of the San Gabriel Fault 72 Castaic Hills Fault 72 San Gabriel Fault "C" (?) 73 San Gabriel Fault "B" 75 Stage III Structures 81 Dry Canyon Syncline and Dry Canyon Anticline 81 Townsend Syncline 81 Loma Verde Antichne 82 North and South Hasley Canyon Synclines 82 Oak Canyon Anticline 83 Normal Fault in Castaic Hills 83 Has ley Fault 84 Villa Canyon Structure of Weber (1979) 85 San Gabriel Fault "B" 86 SEISMICITY 88 SEISMIC AND GROUND RUPTURE HAZARDS 90 GEOLOGIC HISTORY 91 REFERENCES CITED 99 APPENDIX I 111 APPENDIX II 122 LIST OF ILLUSTRATIONS Figure Page 1 Regional geologic setting of the Castaic area 2 2 Generalized geologic map of the Castaic area 3 3 Wells which penetrate basement in the Castaic area 7 4 Oil fields in the Castaic area 11 Generalized columnar section west of the San Gabriel fault 13 Generalized columnar section east of the San Gabriel fault 15 Major structures ui the Castaic area 62 Stage I structures 63 Stage U structures 64 10 Stage III structures 65 hA Diagrai parallel to the San Gabriel fault showing offset of the 700 foot isopach and the base of the Pico Formation 80 11B Diagram parallel to the San Gabriel fault showing two possible displacement vectors of the base of the Pico Formation 80 Plate I Geologic map of the Castaic area II Well base map and cross section locations IIIStructure contour map of the base of the Saugus Formation IV Structure contour map of the base of the Pico Formation V Structure contour map of the base of the Tows ley Formation VI Isopach map of the Pico Formation VII Strucure contour map of San Gabriel fault "B", Castaic Hills fault, 3nd normal fault in Castaic Hills VIII Structure contour map of the Has Ley fault, and paleogeology at the base of the Hasley conglomer- ate (base Towsley) IX Cross Section A-A' X Cross Section B-B' XI Cross Section C-C, XII Cross Section D-D' XIII Cross Section E_Et XIV Cross Section F-F' XV Cross Section G-G' XVI Cross Section H-H1 Plate Pocket XVII Cross Section I-I' XVIII Cross SectionJ-Jt XIX Cross Section K-K1 XX Cross Section L-L' XXI Cross Section M-M' XXII Cross Section N-N' XXIII Cross Section 0-0' XXIV Cross Section P-P' GEOLOGY OF THE VENTURA AND SOLEDAD BASINS IN THE VICINITY OF CASTAIC, LOS