The geology of the San Francisco Bay region

Why does a bit of ocean floor lie on top of Mt. Diablo? Why is Red Rock, that small, knobby island in San Francisco Bay, red? Why is Loma Prieta high? This book is for San Francisco Bay Area residents and visitors who want to explore the geologic world of this spectacular area, to learn about its shapes, colors, and rocky foundations. Doris Sloan illuminates the colorful geologic mosaic that surrounds San Francisco Bay and lucidly explains the complex and fascinating processes that have forged it over millions of years. In a lively and engaging style, Sloan describes forces such as the movement of tectonic plates, erosion, the waves on the coast, and human activity. She provides background information on the processes, time frame, and rocks that are the key to understanding the Bay Area landscape and geologic history, then turns to distinct regions of the Bay Area and to San Francisco Bay itself. * Superbly illustrated with 139 color photographs, 41 drawings, and 29 maps * Covers Alameda, Contra Costa, Marin, Napa, San Francisco, San Mateo, Santa Clara, Solano, and Sonoma counties * Gives clear, nontechnical explanations of complex topics including plate tectonics and the Bay Area's fault systems * Suggests locales in parks and open space preserves to view Bay Area geology in action CONTENTS 7 ACKNOWLEDGMENTS 11 INTRODUCTION 13 1. THE BAY AREA AND THE PROCESSES THAT SHAPE ITS GEOLOGY 19 Time: Human and Geologic 21 Geologic Processes: Shaping the Landscape 28 2. THE PLATE TECTONIC FRAMEWORK 43 The Dance of the Plates 46 California’s Dynamic Past 49 The Bay Area’s Network of Faults 50 Squeezing the Bay Area 58 The Bay Area’s Complex Structure 61 3. THE REMARKABLE ROCKS OF THE BAY AREA 65 The Foundation under Our Feet: The “Basement” Rocks 67 The Younger Rocks: Emerging from the Sea 88 4. MARIN COUNTY: A DIVIDED LANDSCAPE 95 West of the San Andreas Fault 102 Sierra Rocks in the Bay Area? East of the San Andreas Fault 111 The Franciscan Complex ■ The Great Valley Complex ■ The Younger Rocks Special Places to Explore 117 5. SAN FRANCISCO: GEOLOGY BENEATH THE PAVEMENT 127 The Streams and Lakes That Once Were 129 The City on the Dunes 137 Ice Age Dune Sand ■ Modern Sand along the Shore Under the City: The Rocky Foundation 141 Alcatraz Terrane ■ Marin Headlands Terrane ■ San Bruno Mountain Terrane ■ Mélange Zones On Top of the Basement Rocks 148 6. THE BAY AND THE ISLANDS 151 The Estuary and Its Surprises 153 Water That Flows “Upstream” Secrets of the Sediments 159 Early History of the Bay 18 Marshes and Plains around the Bay 164 The Islands in the Bay: The Drowned Landscape 169 7. THE PENINSULA: COAST, REDWOODS, AND BAY 175 The Coastal Landscape 176 The Land Uplifted ■ Down to the Sea Faults That Carve Up the Peninsula 184 8. THE SOUTH BAY 203 The Valley That Was: The Santa Clara Valley 205 South Bay Faults and Structure 212 The South Bay’s Diverse Rocks 216 The Basement Rocks ■ The South Bay Tertiary Rocks: From Sea to Land ■ Volcanic Rocks Special Places to Explore 226 9. THE EAST BAY 235 A Young Landscape 236 The Delta: A Subsided Marsh ■ Creeks That Go the Long Way Round The East Bay Fault System 246 The Hayward Fault Rocks Old and Young 248 The Mesozoic Subduction Record ■ From Sea to Land ■ The Livermore Valley 18 Special Places to Explore 257 10. THE NORTH BAY 271 The Sonoma Coast: Lifted Up and Slumping Down 273 Faults and Fault Slices 281 The Hole in the Head Assembling the North Bay 283 The Basement Rocks ■ Across the Fault ■ After Subduction Ended The North Bay’s Volcanoes 293 The Geysers Rivers and Bay 301 A Special Place to Explore: Goat Rock State Beach 302 Glossary 307 Further Reading 313 Figure and Map Sources 317 Photo Credits 321 Additional Captions 323 Geologic Map Index 325 Index 333 Doris Sloan ; With Photographs By John Karachewski. Includes Bibliographical References (p. 295-298) And Index.