California Rocks!: A Guide to Geologic Sites in the Golden State

California

ROCKS!

A Guide to Geologic Sites in the Golden State

KATHERINE J. BAYLOR

2010

Mountain Press Publishing Company

Missoula, Montana

© 2010 by Katherine J. Baylor

First Printing, May 2010

All rights reserved

Cover image © 2010 by Katherine J. Baylor

Photos © 2010 by Katherine J. Baylor unless otherwise credited

Maps © 2010 by Katherine J. Baylor unless otherwise credited

Library of Congress Cataloging-in-Publication Data

Baylor, Katherine J., 1961–

California rocks! : a guide to geologic sites in the Golden State / Katherine J. Baylor.

p. cm.

Includes bibliographical references and index.

ISBN 978-0-87842-565-5 (pbk. : alk. paper)

1. Geology—California—Guidebooks. 2. California—Guidebooks. I. Title.

QE89.B39 2010

557.94—dc22

2010003529

Printed in Hong Kong by Mantec Production Company

Mountain Press Publishing Company

P.O. Box 2399 • Missoula, Montana 59806

(406) 728-1900

For my favorite young Californians:

Kira, Emily, Vanessa, and Ryan

PREFACE

California’s high mountains, rocky coastlines, inland valleys, stunning beaches, and warm deserts draw visitors from around the globe. This spectacular tableau is the culmination of hundreds of millions of years of geologic processes, from the collision of tectonic plates to volcanic eruptions and earthquakes, to glaciation, sea level changes, erosion, and deposition. The reddish brown, tightly folded rock layers in Golden Gate National Recreation Area? Radiolarian chert. The cluster of peaks that rise out of the Central Valley north of Sacramento? A young volcano known as Sutter Buttes. The steeply tilted rock layers in Devils Punchbowl County Park? A syncline.

California has more than 25 national parks, 270 state parks, and countless hundreds of regional and local parks. In this book, I have summarized the geologic setting of 65 of the parks and special places statewide, with an emphasis on what is visible to the casual observer. The geologic summaries in this book are intentionally short, and telling the complete geologic story of the Golden State is beyond the scope of this book. Readers searching for more in-depth discussion are encouraged to consult the section Further Reading, at the back of the book.

Although the sites listed in this book are nearly all accessible by paved roads, many are in relatively remote areas of California. Invest in high-quality road maps, and know how to use them. Members of the Automobile Association of America (AAA) will find the California sectional map series to be of a scale adequate to reach most of the sites listed in this book. Use computer-based mapping tools with caution.

Nearly every site listed in this book is a protected public space. National, state, and local parks strictly prohibit the collection of rocks, soil, and other natural features. Rock outcrops should be left in their natural state. Rock weathering is a natural process that adds to the beauty of the landscape.

ACKNOWLEDGMENTS

Many people contributed to the success of California Rocks by suggesting sites, reviewing specific sections, and providing photographs. I thank my editor at Mountain Press, Jennifer Carey, and the following individuals: Ken Aalto, Scott Anderson, John Arnold, Randy Bolt, Kristi Britt, Ed Clifton, Susan Davis, Carlos de la Rosa, Joel Despain, Jason DeWall, Julie Donnelly-Nolan, Steve Edwards, Will Elder, Chris Farrar, Cynthia Gardner, Eric Geist, David C. Greene, Don Grine, Ed Guaracha, Jane Hall, Karen Haner, John M. Harris, Lauren Harrison, Brian Hausback, Mark Jorgensen, Brian Ketterer, Kevin Key, Jody Kummer, Mark Langner, Ed Leong, Mary Maret, Dave Marquart, Seth Migdail, Ron Munson, Jeff Nickell, Juventino Ortiz, Charles Paull, Josh Pederson, Roi Peers, David Pryor, Linda Rath, Christina Sherr, Jeanne Sisson, Linda Slater, John Slenter, Doris Sloan, Woody Smeck, Dar Spearing, Bob Spoelhof, Miles Standish, Greg Stock, Phil Stoffer, Michael Strickler, Karl Tallman, Lindsey Templeton, Walter Vennum, Michael Walawender, Xiaoming Wang, Dave Whistler, Carol Witham, and Joe Zarki.

Regions in California Rocks. Numbers correspond to specific sites.

CONTENTS

Preface

Acknowledgments

Geologic Time Scale

Plate Tectonics and California

Northeast California

1. Lava Beds National Monument

Caves in Basalt

2. Mount Shasta

A Stratovolcano

3. Castle Crags State Park

Exfoliation Joints in Granitic Rock

4. McArthur–Burney Falls Memorial State Park

A Spring-Fed Waterfall

5. Lassen Volcanic National Park

Eruptions and Boiling Springs

North Coast

6. Jedediah Smith Redwoods State Park

Josephine Ophiolite

7. Crescent City

Tsunami Country

8. Patrick’s Point State Park

Franciscan Mélange and Younger Rocks

9. Cache Creek Natural Area

The Great Valley Sequence

10. Salt Point State Park

Trace Fossils

San Francisco Bay Area

11. Sonoma Coast State Park

Sea Stacks

12. Calistoga’s Petrified Forest

Petrified Wood

13. Napa Valley

Terroir of Wine

14. Point Reyes National Seashore

The San Andreas Fault and the Rocks It Brought with It

15. Golden Gate National Recreation Area

Radiolarian Chert and Pillow Basalt

16. Sibley Volcanic Regional Preserve

Young Volcanics in the Coast Range

17. Black Diamond Mines Regional Preserve

California Coal

18. Mount Diablo State Park

Trail Through Time

19. Vasco Caves Regional Preserve

Concretions in Sandstone

20. Mavericks Surf Break

Seafloor Topography

21. San Gregorio State Beach

Sea Caves and Trace Fossils

22. Bean Hollow State Beach

Tafoni and Graded Bedding

23. Los Trancos Open Space Preserve

The 1906 Earthquake

24. Almaden Quicksilver County Park

Mercury Mine

Sierra Nevada

25. Sutter Buttes

A Young Volcanic Center

26. Empire Mine State Historic Park

Hard Rock Gold Mine

27. Malakoff Diggins State Historic Park

Hydraulic Mining of Placer Deposits

28. Mather Regional Park

Vernal Pools

29. Lake Tahoe

History of a Basin

30. Grover Hot Springs State Park

Sierra Volcanics

31. California State Mining and Mineral Museum

Gemstones and Gold

32. Yosemite National Park

Sculpting by Water and Ice

33. Kings Canyon National Park

Mineralogy of Granite

34. Sequoia National Park

Caves in Marble

Eastern Sierra

35. Bodie State Historic Park

Gold Mining Ghost Town

36. Mono Lake Tufa State Natural Reserve

Pillars of Limestone

37. Panum Crater

A Very Recent Eruption

38. Devils Postpile National Monument

Columns in a Lava Flow

39. Horseshoe Lake

Carbon Dioxide Tree Kill

40. Hot Creek Geological Site

Hot Geysers in a Cold Creek

41. Convict Lake

A Roof Pendant

Central Coast

42. Castle Rock State Park

Tafoni Weathering of Sandstone

43. Natural Bridges State Beach

Coastal Erosion

44. Carmel River State Beach

Submarine Monterey Canyon

45. Point Lobos State Natural Reserve

The Salinian Block and the Carmelo Formation

46. Morro Bay State Park

A Line of Volcanic Plugs

47. Pinnacles National Monument

A Volcano Split by the San Andreas Fault

South Coast

48. Gaviota State Park

The Monterey Formation

49. Kern County Museum

Black Gold

50. Red Rock Canyon State Park

Miocene Fossils

51. Santa Monica Mountains National Recreation Area

Transverse Ranges

52. Vasquez Rocks Natural Area

Red Conglomerates and Fanglomerates

53. Devils Punchbowl County Park

Folded and Faulted Rocks

54. La Brea Tar Pits

Ice Age Fossils

55. Abalone Cove Shoreline Park

Landslides

56. Crystal Cove State Park

Marine Terraces

57. San Onofre State Beach

Cristianitos Fault

58. Torrey Pines State Natural Reserve

Sedimentary Features along the Beach Trail

59. Mission Trails Regional Park

Mountain of Granite

60. Cuyamaca Rancho State Park

Rocks of the Peninsular Ranges

Deserts

61. Death Valley National Park

Salt Flats in a Closed Basin

62. Mojave National Preserve

Sand Dunes and Volcanic Tuff

63. Joshua Tree National Park

Rock Weathering

64. Salton Sea State Recreation Area

A Saline Lake

65. Anza-Borrego Desert State Park

Flash Floods

Glossary

Site Contact Information

Further Reading

Index

Geographic regions of California

PLATE TECTONICS AND CALIFORNIA

California’s geologic history is best understood in the context of plate tectonics, a well-established theory developed in the 1960s. In the nineteenth century, earlier researchers, such as state geologist Josiah Whitney, were able to document the what, but not the why, of California’s geologic landscape. Whitney, who led the first geologic survey of the state from 1860 to 1864, recognized the importance of fossils, sedimentary layers, and volcanic rocks in California’s unique landscape but didn’t have the tools to explain how all of the elements fit together. To fully appreciate the sites described in this book, you’ll probably find it useful to understand the major elements of plate tectonics and how they help explain the California landscape.

The inner part of the Earth consists of a solid iron-nickel core surrounded by a liquid outer core. Above the core is the mantle, a thick semisolid layer that extends almost to Earth’s surface. At the very surface of the Earth is the crust, a relatively thin layer of hard rock. Only about 3 miles thick in the deep ocean and more than 30 miles thick under high mountain ranges, the Earth’s crust is broken into several large and many smaller pieces, called plates, that move slowly across the mantle. Plate tectonic movement is exceedingly slow, averaging inches per year. Over millions of years, however, the inches add up, leading to today’s distribution of continents. Numerous lines of evidence support plate tectonic theory, including the presence of identical fossils on landmasses now separated by oceans, magnetic data from seafloor rocks, and geophysical information from earthquakes.

Boundaries between the Earth’s plates take three general forms: divergent, convergent, and transform. Divergent plate boundaries occur primarily in the deep ocean, at seafloor spreading centers such as the Mid-Atlantic Ridge and East Pacific Rise. These underwater mountain ranges, invisible to us until the development of sonar mapping technology, are zones of intense volcanic activity. New oceanic crust, primarily the volcanic rock basalt, is created at spreading centers.

Cross section of the Earth —Modified from the U.S. Geological Survey

Convergent boundaries form where collisions occur between two plates. At the collision site between an oceanic plate and a continental plate, oceanic crust, which is denser, is subducted beneath lighter continental rock and becomes incorporated into the mantle. Where two oceanic plates collide, generally the older plate, which is colder and denser, is subducted beneath the younger plate. In a few locations, most notably the Himalayas, continental crust from one plate converges with continental crust from another plate. At these convergences of two continental plates, neither plate is subducted, and the slow collision produces an ever-higher mountain range.

Subduction zones produce a great deal of heat, which melts the adjacent mantle rock and part of the down-going plate, forming magma. Magma that cools and solidifies deep underground forms granite and other intrusive igneous rocks. Magma that erupts from a volcano produces extrusive igneous rocks such as basalt or rhyolite.

The final type of plate boundary, and the most important type for many Californians, is the transform boundary, where two plates