The Rinconada and Related Faults in the Southern Coast Ranges, California, and Their Tectonic Significance GEOLOGICAL SURVEY PROF-ESSIONAL PAPER 981 The Rinconada and Related Faults in the Southern Coast Ranges, California, and Their Tectonic Significance By THOMAS W. DIBBLEE, JR. GEOLOGICAL SURVEY PROFESSIONAL PAPER 981 A study of the Rinconada fault and its relation to other nearby major faults and to the tectonics of the southern Coast Ranges UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1976 UNITED STATES DEPARTMENT OF THE INTERIOR THOMAS S. KLEPPE, Sun-tan GEOLOGICAL SURVEY V. E. McKelvey, Director Library of Congress Cataloging in Publication Data Dibblee, Thomas Wilson The Rinconada and related faults in the southern coast ranges, California, and their tectonic significance. (Geological Survey Professional Paper 981) Bibliography: p. 53-55. Supt. of Docs, no.: I 19.16:981 1. Faults (Geology) California Coast Range. I. Title: The Rinconada and related faults in the southern coast ranges, California. II. Series: United States Geological Survey Professional Paper 981. QE606.5.U6D5 551.8'7 76-608324 For sale by the Superintendent of Documents, U.S. Government Printing Office Washington, D.C. 20402 Stock Number 024-001-02908-1 CONTENTS Page Page Abstract __________________________________________________ 1 Segments of the Rinconada fault Continued Introduction ____________________________________________ 1 Relationship of Rinconada fault to Jolon and related Location of the Rinconada fault __________________ 1 faults __________________ _ 29 Purpose and scope _______________________________ 2 Geophysical expression of the Rinconada fault ____ ____ 32 Acknowledgments-_______________________________ 2 Reliz fault ________________________________________________ 32 Major geologic relations of the Rinconada fault ______________ 2 King City fault ______________________________________ 32 Nomenclature and definition__________________________ 2 Reliz fault in Arroyo Seco area________________________ 33 Regional relations _______________________________ 6 Reliz fault at base of Sierra de Salinas __________________ 34 Concealed position of southwestern border of the Salinian Possible northwestward extension of the Reliz fault _____ 34 block__________________________________ 8 Regional evidence of large strike-slip movement on the Rin- Rock units ________________________________________ 9 conada-Reliz fault zone ____________________________ 36 Crystalline rocks ______________________________ 9 Movements in Quaternary time _______________________ 36 Franciscan rocks __________________________________ 9 Movements in Pliocene time _________________________ 36 Upper Jurassic(?) and Cretaceous marine sedimentary se­ Movements since early Miocene time ____________________ 36 quence _______________________________________ 12 Movements in Oligocenel?) time ___________________ 38 Upper Cretaceous and lower Tertiary marine sedimentary Possible movements in pre-Late Cretaceous time ______ 38 sequence ___________________________________ 12 Strike-slip movement as suggested by configuration of Middle Tertiary sedimentary sequence ______________ 13 buried surface of basement complex ________________ 40 Upper Tertiary sedimentary sequence ________________ 16 Regional tectonics along and near the Rinconada-Reliz fault Valley sediments ____________________________ 16 zone ________________________-_-_--__-__--_--____---- 40 Surficial deposits ______________________________ 19 Concepts of tectonic evolvement of the Coast Ranges ____ 40 Segments of the Rinconada fault __________________________ 19 Tectonic pattern _______________________________ 42 Rinconada fault (Nacimiento segment) from San Rafael Tectonic features of the east strip ____________________ 44 Mountains to Pozo area ___------._______________-_.____ 19 Tectonic features of the west strip _________________ 44 Other faults near and possibly related to the Nacimiento Regional tectonic analysis ______________________________ 46 segment of the Rinconada fault ____________________ 20 Regional significance of the Rinconada-Reliz fault zone _ 48 Rinconada fault (Rinconada segment) from Rinconada mine Effect of Rinconada-Reliz fault zone on physiography and drain­ to Paso Robles _________________________ 21 age ____________________________________ 52 Rinconada fault (San Marcos segment) from Paso Robles to Possible seismic activity___________________________ 52 San Antonio Reservoir ____________________________ 23 References cited _________________________________ 53 Rinconada fault (Espinosa segment) from San Antonio Res­ ervoir to Reliz Canyon ______________________ 25 ILLUSTRATIONS Page FIGURE 1. Index map showing positions of the Rinconada and Reliz faults relative to the Salinian block and the San Andreas fault ______________________________________________________________ 2 2. Map showing physiographic features and drainages along and near the Rinconada and Reliz faults ____ __ __ 3 3. Map showing nomenclature of some major faults in part of southern Coast Ranges ____ ____________ _ 5 4. Map showing geologic setting of the Rinconada and Reliz faults ______________________________________________ 7 5. Diagram showing major rock units of the Coastal block within area of figures 1, 2 and 4 _____ ________________ 10 6. Diagram showing major rock units of the Salinian block within area of figures 1, 2 and 4__-__-__-_____ __ ---_ 11 7-21. Maps showing: 7. Geology along and near the Rinconada fault (Nacimiento segment) from Big Pine Mountain to Timber Peak _____________________________________________________________ 17 8. Geology along and near the Rinconada fault (Nacimiento segment) from Timber Peak to Pozo ____________ 18 9. Geology along and near the Rinconada fault (Rinconada segment) from the Rinconada mine to Paso Robles ____ 22 10. Geology along and near the Rinconada fault (San Marcos segment) from Paso Robles to San Antonio Reser­ voir ______________________________________________________________________________________________ 24 11. Stream-channels deflected possibly by right-lateral movement on the Rinconada fault (San Marcos segment) northwest of Paso Robles ________________________________________________ ____ __ __ 26 12. Geology along and near the Rinconada fault (Espinosa segment) between Lockwood and Salinas Valleys __ 27 in IV CONTENTS FIGURES 7-21. Maps showing Continued Page 13. Geology along and near the Rinconada fault (Espinosa segment) and Reliz fault, near King City and Greenfield __________________________________________________________________________________ 28 14. Stream channels of canyons deflected possibly by right-lateral movement of the Rinconada fault (Espinosa segment) near Lockwood ____________________________________________________________________ 30 15. Geology of the northern Santa Lucia Mountains, a segment of the Salinian block elevated on the Reliz fault and many other parallel faults ____-___-_____-___-______________-______________---_----_-____-___ 35 16. Inferred displacement of lower Pliocene (unit 1, Pancho Rico Formation) and upper Miocene (unit 2, Santa Margarita Formation) by right lateral strike-slip movement on the Rinconada fault______________ 37 17. Pre-Oligocene rocks of the Salinian block, possibly displaced by right-lateral movement of the Rinconada- Reliz fault zone _______________________________________________------_---__-____-___________ 39 18. Inferred configuration of buried surface of crystalline basement complex along Rinconada-Reliz fault zone from Paso Robles to Greenfield ________________________________________ 41 19. Right-slip tectonics and compressive upheaval along the Espinosa segment of the Rinconada fault ___ __ 42 20. Major tectonic features of the southern Coast Range region in vicinity of the Rinconada-Reliz fault zone __ 43 21. Geology of the upper Nacimiento River area and vicinity ___________________________ _ 47 22. Block diagram illustrating mechanics of conversion of strike-slip movement along a high angle fault into compressive uplift of one block as fault terminates ____--_---_-__-______-_____-__-__-________________________________ 43 23. Map showing inferred tectonic movements in vicinity of northern Santa Lucia Mountains showing conversion of right-slip movements near ends of Rinconada-Reliz fault zone and San Gregorio fault into crustal compression and uplift of intervening area to form these mountains ________________________________________________ 50 24. Map showing inferred tectonic movements in vicinity of Sierra Madre Mountains and Pine Mountain, showing inferred conversion of right-slip movements near ends of the Rinconada and San Gabriel faults to crustal com­ pression to form these ranges ______________________________________________-_--_-__-__-___-------_-____ 51 THE RINCONADA AND RELATED FAULTS IN THE SOUTHERN COAST RANGES, CALIFORNIA, AND THEIR TECTONIC SIGNIFICANCE By THOMAS W. DIBBLEE, JR. ABSTRACT The northern part of the strip within the Salinian block east of the The Rinconada fault near Santa Margarita, as depicted on the Rinconada-Reliz fault zone reacted to stress during late Cenozoic Geologic Map of California, is a northwest-trending high-angle fault time as a rigid block of crystalline basement that was tilted slightly about 40 km (26 mi) long that in part separates terranes with differ­ southwestward from an axis adjacent to the San Andreas fault to ent basement complexes. The terrane on the northeast is part of the form the Gabilan uplift and Salinas Valley. The