California's Amazing Geology

Donald R. Prothero

• Publisher: CRC Press
• Year: 2017
• ISBN:
  9781498707954
• Edition: 1
• Topic: Physical Sciences
• Subtopic: Geology & Earth Sciences

California has some of the most distinctive and unique geology in the United States. It is the only state with all three types of plate boundaries, an extraordinary history of earthquakes and volcanoes, and it has many rocks and minerals found nowhere else. The Golden State includes both the highest and lowest point in the continental US and practically every conceivable geological feature known. This book discusses not only the important geologic features of each region in California, but also the complex geologic four-dimensional puzzle of how California was assembled, beginning over 2 billion years ago. The author provides up-to-date and authoritative review of the geology and geomorphology of each geologic province, as well as recent revelations of tectonic history of California's past. There are separate chapters on some of California's distinctive geologic resources, including gold, oil, water, coastlines, and fossils. An introductory section describes basic rock and mineral types and fundamental aspects of plate tectonics, so that students and other readers can make sense of the bizarre, wild, and crazy jigsaw puzzle that is California's geological history.

PART ONE

Fundamentals of Geology

CHAPTER ONE

The Golden State

Growing up in northern California has had a big influence on my love and respect for the outdoors. When I lived in Oakland, we would think nothing of driving to Half Moon Bay and Santa Cruz one day and then driving to the foothills of the Sierras the next day.

TOM HANKS

Of all the 50 states of the United States, California has some of the most amazing geology and natural history. It has rocks dating back 1.8 billion years (Ga), as well as volcanoes that erupted just a century ago. It has a wide spectrum of minerals and rocks, from ancient volcanoes to young ones, granitic rocks that formed the mighty Sierra Nevada range, and peculiar rocks in the Coast Ranges found nowhere else in the United States. It has the highest mountains in the lower 48 states (Mt. Whitney, 4421 m, or 14,495 feet, above sea level) and the lowest point in the Americas (Badwater in Death Valley, 86 m, or 283 feet, below sea level). Both are within a 135-mile running distance for ultramarathoners in the Badwater Marathon. Death Valley is one of the hottest and driest places on earth, reaching 60°C (134°F) and receiving less than 2.5 cm (1 inch) of average annual rainfall. The High Sierras are one of the snowiest places in the United States, with recorded snowfalls on Tamarack Mountain reaching 23 m (76 feet) in 1 year, 10 m (33 feet) in a single month, and 11 m (37 feet) on the ground at one time. California has the highest waterfall in North America (Yosemite Falls, 869 m, or 2850 feet, of sheer drop). After Mt. Rainier, Mt. Shasta is the second tallest active volcano in the United States, reaching 4317 m (14,162 feet). Until the eruption of Mt. St. Helens in 1980, Mt. Lassen was the most recent active volcano in the lower 48 states, last erupting in 1914–1921.

Many of California’s other geological features are extraordinary as well. It experienced the largest earthquakes in the United States outside of Alaska, including the 1906 San Francisco quake (magnitude 8.2), the 1872 Lone Pine quake (magnitude 8.25), and the 1857 Ft. Tejon quake (magnitude 8.2), as well as many smaller quakes, such as the 1994 Northridge quake (magnitude 6.7). One of the biggest explosive volcanic eruptions in the history of the planet occurred about 750,000 years ago when Long Valley Caldera (near Mammoth Mountain ski resort and Bishop in the Owens Valley) blew its top and scattered 521 km³ (125 cubic miles) of ash across the entire western United States, reaching eastern Nebraska and Kansas. California is also one of the biggest producers of oil and gas in the United States, as well as yielding major deposits of gold, mercury, chromite, rare earth elements, and many other important natural resources.

Its natural history is also remarkable. It has the largest living things on earth (the giant sequoias), the tallest on earth (the coast redwoods), and some of the oldest living things on earth (the bristlecone pines in the White Mountains are up to 10,000 years old). It has ecological regions ranging from coastal rain forests to dry deserts to snowcapped mountains to some of the most picturesque coastlines on earth. It is home to some of the largest mammals, including large elk, cougar, and deer. There are immense elephant seals on its beaches, as well as tiny rodents and endemic species of foxes on its offshore islands. The grizzly bear once roamed widely over the whole state, which is why the state has the “Bear Flag” and the bear mascot of the University of California campuses. Due to the wide range of habitats and huge area, California is host to one of the widest diversities of birds, reptiles, amphibians, and fish in North America, as well as extremely diverse plant habitats, from misty redwood forests to cactus-filled desert.

California can claim many other distinctions as well, which make it one of the most important states. By population, California is the largest state in the United States (38 million people in the 2010 census), and it is the third largest state in area. In fact, if California were an independent nation, it would be the 35th largest nation in the world by population. This status as the largest state by population means California has major political clout: the largest delegation in Congress (53 representatives) and the most electoral votes in presidential elections (55). By itself, California provides about 20% of the electoral votes needed to win the presidency.

Even individual counties in California are larger than many states. San Bernardino County is the largest in the United States by area (52,070 km², or 20,105 square miles). It is bigger than nine states (Maryland, Hawaii, Massachusetts, Vermont, New Hampshire, New Jersey, Connecticut, Delaware, and Rhode Island), so if it were a state, it would be the 43rd largest in area. Los Angeles County has the largest population of any US county (more than 9.8 million people), more people than 42 of the 50 states. If Los Angeles County were to become a state, it would be the ninth largest in the U.S. by population.

California is home to 3 of the 10 largest cities in the United States, more than any other state except Texas, which also has 3. These include Los Angeles (number 2) and, surprisingly, San Diego (number 8) and San Jose (number 10). Although people think of San Francisco as huge, it is only number 13 on the list. Fresno is the 34th largest U.S. city, Sacramento the 35th, Long Beach the 36th, and Oakland the 47th. That makes 8 of the top 50 largest cities, more than any other state. The Los Angeles Metropolitan Area is the second largest in the United States after New York City, with 18 million people, larger than all but a few states. The San Francisco Bay Metropolitan Area ranks the 5th largest with 8 million, and the San Diego area is the 18th largest with 3 million.

This huge population and size is matched by incredible economic power, from the tech wizards of Silicon Valley to the center of the entertainment industry in Hollywood and environs (movies, TV, and music especially) to the incredible wealth in oil and agricultural products. California is the largest agricultural state in the union, producing 99% of all the almonds, walnuts, and pistachios; 95% of the broccoli and strawberries; 90% of the grapes and tomatoes; and 74% of all the lettuce consumed in the United States. California’s gross domestic product (more than $14 trillion) is larger than that of all but eight countries in the world, so if California were a nation, it would be the world’s ninth largest economy. When the governor of California speaks at international meetings of world leaders, he has more clout than any American official except the president or vice president. That influence has been translated into California leading the United States in clean energy policies, laws against air pollution, and many other progressive stances, such as political reform. California was the first state in the nation (and still one of the few) to institute measures such as initiatives (where voters can put measures on the ballot without their politicians), referendums, and recalls.

GEOGRAPHIC AND GEOLOGIC PROVINCES

California is particularly unusual and complicated in its geography and geology, especially compared to some of the flat states in the Midwest. Many of these states (such as Michigan or Kansas) have almost no mountains or even tall hills, and the geology underlying them is fairly simple, with broad shallow dish-shaped basins and nearly flatlying beds across most of the state. By contrast, California is the only state that has all three types of plate tectonic boundaries (subduction zone in the north, transform boundary along the San Andreas fault zone, and spreading ridge in the Salton Trough and Gulf of California) within it. It is also the only U.S. state that straddles two tectonic plates.

Consequently, California has remarkably distinct geographic regions (Figure 1.1a), each of which has an almost entirely different geology from the other regions (Figure 1.1b). Each region has its own complicated geologic history, which we will look at one region at a time to better understand their local stories, before we try to assemble the complete jigsaw puzzle of California in Chapter 15. We start with the regions with the simplest geology, such as the Cascade Range and Modoc Plateau, and then move to more complex regions, such as the Basin and Range and Sierras, before finishing with the wild and crazy geology of the Coast Ranges and Transverse Ranges.

Figure 1.1. (a) Digital elevation map of California. (b) Geologic map and geographic provinces of California, showing the geologic complexity of the state. (Courtesy of California Division of Mines and Geology.)

The major geographic provinces of California are shown in Figure 1.1. We discuss each of them in the following chapters.

CHAPTER TWO

Building Blocks

MINERALS AND ROCKS

The rock I’d seen in my life looked dull because in all ignorance I’d never thought to knock it open. People have cracked ordinary pegmatite—big, coarse granite—and laid bare clusters of red garnets, or topaz crystals, chrysoberyl, spodumene, emerald. They held in their hands crystals that had hung in a hole in the dark for a billion years unseen. I was all for it. I would lay about me right and left with a hammer, and bash the landscape to bits. I would crack the earth’s crust like a piñata and spread to the light the vivid prizes in chunks within. Rock collecting was opening the mountains. It was like diving through my own interior blank blackness to remember the startling pieces of a dream: there was a blue lake, a witch, a lighthouse, a yellow path. It was like poking about in a grimy alley and finding an old, old coin. Nothing was as it seemed. The earth was like a shut eye. Mother’s not dead, dear—she’s only sleeping. Pry open the thin lid and find a crystalline intelligence inside, a rayed and sidereal beauty. Crystals grew inside rock like arithmetical flowers. They lengthened and spread, adding plane to plane in awed and perfect obedience to an absolute geometry that even the stones—maybe only the stones—understood.

ANNIE DILLARD
An American Childhood

Before we can discuss the details of California geology, we must briefly cover the fundamentals. For those who have already taken an introductory course on geology, this chapter may mostly be review, or can be skipped altogether. However, this book is often used for college courses that assume no previous exposure to geology. In addition, many nongeologist readers of this book will be baffled if they encounter the names of important rocks and minerals without the proper explanation, so these are introduced here.

However, the material in this chapter is important to understand even if you have some geology background. California has some really unusual minerals and rocks, such as its state rock, serpentine, or some of its other peculiar rocks, such as ribbon cherts, blueschist, ophiolites, weird evaporite minerals, diatomites, and many others that are rare or unknown in most other states.

In the next few chapters, we also cover the basics of tectonics and structural geology, seismology, and other principles of geology that are usually covered in an introductory college course. When we discuss the geologic provinces, everyone should have at least some background to follow the discussion.

ATOMS AND ELEMENTS

First, let’s quickly review the most basic principles of physics and chemistry. All matter is made of atoms, which are the smaller particle of matter that has the properties of a given element. For example, atoms of the element gold have its characteristic properties (such as its high density), but if you break a gold atom into its subatomic particles, they no longer have those same properties. The three main subatomic particles are the proton (which has a +1...