Geology of the San Francisco Bay Region PDF
Preview Geology of the San Francisco Bay Region
CALIFORNIA NATURAL HISTORY GUIDES GEOLOGY OF THE SAN FRANCISCO BAY REGION California Natural History Guides Phyllis M. Faber and Bruce M. Pavlik, General Editors GEOLOGY of the SAN FRANCISCO BAY REGION Doris Sloan With photographs by John Karachewski UNIVERSITY OF CALIFORNIA PRESS Berkeley Los Angeles London Dedicated to the late Clyde Wahrhaftig,mentor and friend, who taught me how to read the landscape. University ofCalifornia Press,one ofthe most distinguished university presses in the United States,enriches lives around the world by advancing scholarship in the humanities,social sciences,and natural sciences.Its activities are supported by the UC Press Foundation and by philanthropic contributions from individuals and institutions.For more information,visit www.ucpress.edu. California Natural History Guide Series No. 79 University ofCalifornia Press Berkeley and Los Angeles,California University ofCalifornia Press,Ltd. London,England © 2006 by the Regents ofthe University ofCalifornia Library ofCongress Cataloging-in-Publication Data Sloan,Doris,1930–. The geology ofthe San Francisco Bay region / Doris Sloan ;photography by John Karachewski. p.cm.— (California natural history guides ;79) Includes bibliographical references and index. ISBN-13,978-0-520-23629-5 (cloth,alk.paper),ISBN-10,0-520-23629-7 (cloth,alk.paper) ISBN-13,978-0-520-24126-8 (pbk.,alk.paper),ISBN-10,0-520-24126-6 (pbk.,alk.paper) 1. Geology—California—San Francisco Bay Area. I.Title.II.Series. QE90.S12S58 2006 557.94'61--dc22 2004014703 Manufactured in China 10 09 08 07 06 10 9 8 7 6 5 4 3 2 1 The paper used in this publication meets the minimum requirements of ANSI/NISO Z39.48–1992 (R 1997) (Permanence ofPaper).I Cover:View south across Golden Gate toward the Presidio ofSan Francisco. Ridge ofFranciscan chert in foreground.Photograph by John Karachewski. The publisher gratefully acknowledges the generous contributions to this book provided by the Gordon and Betty Moore Fund in Environmental Studies and the General Endowment Fund ofthe University ofCalifornia Press Foundation. CONTENTS Acknowledgments xi Introduction xiii 1. THE BAY AREA AND THE PROCESSES THAT SHAPE ITS GEOLOGY 1 Time: Human and Geologic 3 Geologic Processes: Shaping the Landscape 10 At the Surface: Weathering and Erosion ■ Where Sea Meets Land ■The Sand on (and off) the Beach 2. THE PLATE TECTONIC FRAMEWORK 25 The Dance of the Plates 28 California’s Dynamic Past 31 The Bay Area’s Network of Faults 32 Squeezing the Bay Area 40 The Bay Area’s Complex Structure 43 3. THE REMARKABLE ROCKS OF THE BAY AREA 47 The Foundation under Our Feet: The “Basement” Rocks 49 The World-Famous Franciscan Complex ■ Assembling the Franciscan ■Great Valley Complex■Salinian Complex: Visitor from Down South The Younger Rocks: Emerging from the Sea 70 Tertiary Volcanic Rocks ■At the Top of the Heap 4. MARIN COUNTY: A DIVIDED LANDSCAPE 77 West of the San Andreas Fault 84 Sierra Rocks in the Bay Area? East of the San Andreas Fault 93 The Franciscan Complex ■The Great Valley Complex ■The Younger Rocks Special Places to Explore 99 The Marin Headlands ■Ring Mountain: The Bay Area’s Unusual Metamorphic Rocks ■Mount Tamalpais: Cross Section through Subduction 5. SAN FRANCISCO: GEOLOGY BENEATH THE PAVEMENT 109 The Streams and Lakes That Once Were 111 The City on the Dunes 119 Ice Age Dune Sand ■Modern Sand along the Shore Under the City: The Rocky Foundation 123 Alcatraz Terrane ■Marin Headlands Terrane ■ San Bruno Mountain Terrane ■Mélange Zones On Top of the Basement Rocks 130 6. THE BAY AND THE ISLANDS 133 The Estuary and Its Surprises 135 Water That Flows “Upstream” Secrets of the Sediments 141 Early History of the Bay Marshes and Plains around the Bay 146 The Islands in the Bay: The Drowned Landscape 151 7. THE PENINSULA: COAST, REDWOODS,AND BAY 157 The Coastal Landscape 158 The Land Uplifted ■Down to the Sea Faults That Carve Up the Peninsula 166 The Basement Rocks ■A Record of Past Seas ■The Youngest Rocks of the Peninsula 8. THE SOUTH BAY 185 The Valley That Was: The Santa Clara Valley 187 South Bay Faults and Structure 194 The South Bay’s Diverse Rocks 198 The Basement Rocks ■The South Bay Tertiary Rocks: From Sea to Land ■ Volcanic Rocks Special Places to Explore 208 Alum Rock Park: The South Bay’s Hot Spring Resort ■Almaden Quicksilver County Park 9. THE EAST BAY 217 A Young Landscape 218 The Delta: A Subsided Marsh ■Creeks That Go the Long Way Round The East Bay Fault System 228 The Hayward Fault Rocks Old and Young 230 The Mesozoic Subduction Record ■ From Sea to Land ■The Livermore Valley Special Places to Explore 239 Mount Diablo State Park ■Black Diamond Mines Regional Preserve ■The East Bay Hills 10. THE NORTH BAY 253 The Sonoma Coast: Lifted Up and Slumping Down 255 Faults and Fault Slices 263 The Hole in the Head Assembling the North Bay 265 The Basement Rocks ■Across the Fault ■ After Subduction Ended The North Bay’s Volcanoes 275 The Geysers Rivers and Bay 283 A Special Place to Explore: Goat Rock State Beach 284 Glossary 289 Further Reading 295 Figure and Map Sources 299 Photo Credits 303 Additional Captions 305 Geologic Map Index 307 Index 315
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