Geology of the San Francisco Bay Region

Geology of the San Francisco Bay Region

Doris Sloan
With photographs by John Karachewski
Copyright Date: 2006
Edition: 1
Pages: 360
https://www.jstor.org/stable/10.1525/j.ctt1pngwj
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  • Book Info
    Geology of the San Francisco Bay Region
    Book Description:

    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

    eISBN: 978-0-520-93781-9
    Subjects: Biological Sciences

Table of Contents

  1. Front Matter
    (pp. i-vi)
  2. Table of Contents
    (pp. vii-x)
  3. ACKNOWLEDGMENTS
    (pp. xi-xii)
  4. INTRODUCTION
    (pp. xiii-xvii)

    Geology is a lens through which we can see the world around us in a new dimension. Knowing the name of a wildflower makes it our friend. Knowing that the bulbous black rock at Point Bonita was formed in the deep sea and has traveled thousands of miles across the Pacific, makes it part of us. So, too, understanding why Red Rock is red, why Loma Prieta is high, why a bit of ocean floor lies on top of Mount Diablo, enriches our connection to the earth. This book is for the San Francisco Bay Area resident or visitor who...

  5. CHAPTER 1 THE BAY AREA AND THE PROCESSES THAT SHAPE ITS GEOLOGY
    (pp. 1-23)

    Some of the most interesting geology in the world is found in our backyard. Here you can see almost every type of geologic process in action. The Bay Area is a colorful geologic mosaic, its tiles composed of a great variety of rocks, its patterns arranged and then rearranged by active faulting. Soften the edges of the tiles through the pounding of the ocean waves or the slump of a landslide, put a magnificent bay into the center of the mosaic, and you have a world-class geologic setting.

    The Bay Area (map 1) holds many geologic surprises. The familiar hills...

  6. CHAPTER 2 THE PLATE TECTONIC FRAMEWORK
    (pp. 25-45)

    Plate tectonic processes are fundamental to the geology of the Bay Area. Every aspect of our landscape—the hills and valleys, the underlying rocks, the earthquakes that occasionally shake us—is the result of living at an active boundary between the North American and Pacific tectonic plates. Because much of the dynamic geology on our planet takes place at plate margins, we have a front-row seat in the tectonic theater. We live along the “Pacific Ring of Fire,” the zone of active earthquakes and volcanoes that circles the Pacific Ocean.

    “Tectonics” refers to movements of the earth’s lithosphere, which consists...

  7. CHAPTER 3 THE REMARKABLE ROCKS OF THE BAY AREA
    (pp. 47-74)

    The world-famous bay area rocks tell a geologic story that reads like a Russian novel with a very large cast of characters. Because of our plate tectonic history, we have a crazy-quilt pattern of rocks almost defying description and order. Bay Area rocks are not piled up in a tidy sequence of units, like the Grand Canyon’s “layer-cake” geology, with older rocks below and younger above. The Bay Area’s rock complexity is the result of movement along ancient and young faults over millions of years. A glance at the geologic map (map 2) shows you what an extraordinary mosaic of...

  8. CHAPTER 4 MARIN COUNTY: A Divided Landscape
    (pp. 77-107)

    The geology of marin county is remarkable for its variety and significance. Here, within a few hundred square miles, we can decipher the dramatic plate tectonic history of the Bay Area and observe the recent activity of one of the world’s major faults, the San Andreas Fault. We can learn about past geologic events and the processes that are actively shaping the landscape today. Marin County (map 5) provides us an opportunity to explore a wide range of geologic processes, rock types, and scenery in a magnificent setting.

    The story told by the rocks of Marin County (map 6) spans...

  9. CHAPTER 5 SAN FRANCISCO: Geology beneath the Pavement
    (pp. 109-131)

    The geology hidden beneath the city of San Francisco (map 11) tells a story of subduction, of rocks that have traveled thousands of miles to the Golden Gate, and of sand dunes that once stretched from Ocean Beach to the bay. The geology pokes so firmly through the cultural overlay (map 12) that with a little walking around one can learn a great deal, not only about the City’s geology, but also about the Bay Area’s early geologic history. The City’s parks and shoreline, where the underlying Franciscan Complex bedrock is exposed in all its variety and beauty, provide excellent...

  10. CHAPTER 6 THE BAY AND THE ISLANDS
    (pp. 133-155)

    San francisco bay is the jewel in the heart of the Bay Area, a delight to the eye for the millions who live along its shore, and essential to the Bay Area’s economic life. The bay (map 14) is also full of geological surprises.

    The bay is connected to the Pacific Ocean through the Golden Gate, so named by an early California explorer, General John C. Fremont, in reference to Chrysoceras, the harbor of Byzantium. Although the California coast was sailed by many explorers, traders, and pirates after the first explorations in the sixteenth century, San Francisco Bay itself was...

  11. CHAPTER 7 THE PENINSULA: Coast, Redwoods, and Bay
    (pp. 157-183)

    The peninsula affords Bay Area residents many splendid opportunities to explore the spectacular beaches, scenery, and rocks of San Mateo County (map 15). Three very different geologic landscapes call to the visitor: the narrow coastline with magnificent tidepools and sandy beaches, the mountains that form the forested backbone of the Peninsula, and the gently sloping urbanized plain and wetlands along San Francisco Bay. The San Andreas Fault cuts a broad swath through the Peninsula and occasionally sends earthquakes rattling across the Bay Area. Only a few roads cross from coast to bay, giving much of the Peninsula a sense of...

  12. CHAPTER 8 THE SOUTH BAY
    (pp. 185-215)

    For most bay area residents, mention of the South Bay calls up a picture of the urbanized bay plain at the southern end of San Francisco Bay: Silicon Valley, a web of interlaced freeways, heat, and smog. But get past the urban sprawl and you find exceptionally interesting geology never suspected by freeway drivers. Beyond the cityscape are rolling hills and mountains, rivers and reservoirs, ranches, horses, grapes, and extensive open space (map 18). Just a few minutes off any freeway can take you on a trip into the past, geologically and culturally. The many parks in the area provide...

  13. CHAPTER 9 THE EAST BAY
    (pp. 217-251)

    Driving the back roads through the peaceful hills and valleys of the East Bay (map 22), you would not guess how young and dynamic this landscape is. Even in the geologically complicated Bay Area, the East Bay stands out for its fault activity, diversity of rocks, and geologic variety (map 23). The hills of Alameda and Contra Costa Counties are at most a few million years old and are still going up. And the rock record preserves much of the Bay Area’s dramatic geologic history. In particular, here we can see the changes from a colliding to a sliding plate...

  14. CHAPTER 10 THE NORTH BAY
    (pp. 253-287)

    From a magnificent foggy coastline to the hot Central Valley, the three northern counties of the Bay Area—Sonoma, Napa, and Solano—are a microcosm of the Bay Area’s complex geology (maps 26, 27). Explore the uncrowded back roads, stop at interesting road cuts, or walk the beaches along the coast to experience the wide range of processes that created the geologic mosaic of the North Bay. Along the coast, crashing waves and the San Andreas Fault greet you; volcanic hot springs beckon inland. And the dynamic early history of the Bay Area is revealed in rocks across the area....

  15. GLOSSARY
    (pp. 289-294)
  16. FURTHER READING
    (pp. 295-298)
  17. FIGURE AND MAP SOURCES
    (pp. 299-302)
  18. PHOTO CREDITS
    (pp. 303-304)
  19. ADDITIONAL CAPTIONS
    (pp. 305-305)
  20. GEOLOGIC MAPS INDEX
    (pp. 307-313)
  21. INDEX
    (pp. 315-335)
  22. Back Matter
    (pp. 337-340)