cI an tell you exactly where I was at 5:04 p.m. October 17, 1989, when the Loma Prieta earthquake unleashed the equivalent of thousands of hydrogen bombs' worth of energy in 15 seconds. Almost every Bay Area resident I know who was there 20 years ago has a story. I know a lot of people who were late to get on the Bay Bridge, which partially collapsed. Had I been out on the roads on my bike, I might have been killed. This is sort of the Northern Californian equivalent of asking people where they were when JFK got shot.

Only, despite the indelible place it has in individual and collective memory, for most people almost all lessons about it went unlearned. These lessons form the basis of Marc Reisner's A Dangerous Place: California's Unsettling Fate. Reisner is best remembered for his Cadillac Desert, a history of the wild expansion of hydrologically unsustainable California megalopolises and their alternately clownish, cartoonishly evil and foolhardy exploitation of water.

The first third of the book recounts a truncated version of this story, notably the history of corrupt and inept hydrological management of Los Angeles. Those who thought the irrigation story line in the movie Chinatown was fictional will be surprised to see how faithfully it follows the very real venality of the city fathers. More importantly, they'll be baffled to realize that even this skulduggery in the 1930s came after what should have been the city's expiration date on expansion.

Bluntly, Los Angeles should not be, and it should not have been as it was even 80 years ago. As Reisner puts it,

One has to wonder what went on in the minds of southern California's growth lobby as they set out to make Los Angeles the largest city on the planet. The semi-arid basin that they were conjuring into the West's first megalopolis, in the late nineteenth century, had enough water flowing in its rivers, and accumulating in its aquifers, to grow at the rate it was growing for perhaps twenty more years. Then, had all irrigation farming ceased, growth could have continued for another couple of decades. At that point one would have had to ban irrigation on lawns, and in parks. With today's population, even with all outdoor water use banned—no swimming pools—the basin's local sources might permit everyone a bath once a month—in wet years. (p. 48)

Instead, LA pumped water from Arizona, relying for decades on California's larger number of congressmen to outmuscle Arizona in the House of Representatives and keep them from reclaiming their water. Today, it's desperately reliant on water from California's Delta basin, east of the San Francisco Bay Area. It's important to remember this, because the Delta basin, due to years of irrigation, has become a series of semisolid levees, marshland that has geologic definition only due to "fill." The problem is, fill fares very poorly in an earthquake due to something called liquefaction. Fill

is land in the loosest sense of the word. When stressed badly enough, it doesn't behave like land. Semi-saturated, unconsolidated soils slow down seismic waves broadcast by strong earthquakes. As the seismic energy is delayed, shaking amplifies. If the shaking is strong enough, trillions of soil particles lose their cohesiveness. Water within loose sandy soils increases in pressure, to the point where soil particles begin to float and the land liquefies. To appreciate the dynamics of seismo-liquefaction... you might put a firm slab of Jell-O in a saucepan, put the saucepan on a burner, and light the flame. (ibid)

Understanding the properties of fill and the structure of the Delta becomes important in the second part of Reisner's book, which covers an understanding of plate tectonics and how they will apply in the inevitable (and overdue) "Big One," which itself is covered in an extended hypothetical in part three. Of the Delta, he writes:

For more than a century, Delta farmers had been working the most oxidable, and ephemeral, of soil types: peat. As a result, an area thirty times the size of Manhattan had subsided ten to twenty feet below sea level. What you had there now was a vast empty reservoir, a man-made hole in the California landscape. With levee protection lost, the below-sea-level Delta would become, in effect, a vacuum, which nature abhors. Water would pour in there as it would down a manhole. A lot of it would be saltwater sucked in from the bay. If a strong tide was pushing in when the levees failed, things would be that much worse. If it was summer or fall and freshwater outflow through the Delta was meager, it would be worst still. Half of the water supply of greater Los Angeles, San Diego, and the San Joaquin Valley goes through the Delta. Two-thirds of greater San Jose's—which is to say, much of Silicon Valley's—water comes from the Delta. Within hours or days, all that water would be unusable and undrinkable.... (p. 98)

Part three of Reisner's book is horrifying, and it's tempting to think that the book's subtitle of "California's Unsettling Fate" is less a means of muting this horror than of piling cruelly mordant wit atop what he sees as a fatal and catastrophic failure of vision. Because there are very few places to turn in the book that aren't frightening. His hypothetical envisions an over-7.0 quake along the Hayward fault. Not only might it disrupt water and imperil lives for tens of millions in LA, San Diego, the valley and the Bay Area, but the blow to American agriculture would number in the billions. And the impacts on the Bay Area directly aren't much better. San Francisco Bay is now only two-thirds its original size. The rest?—fill, on which sit hospitals, highway 101, parts of the Bay Bridge and countless homes.

The cruelest fact is that none of this is a secret. The dangers of fill were being taught in elementary school classrooms in the 1980s. Reisner's hypothetical is much more of an inevitable than a thought exercise. He probably won't have gotten all the details right, but it hardly matters. His book is engrossingly terrifying. It's a brief, captivating, deeply unnerving look at how tens of millions of Americans willfully live in a place whose continued existence is totally unnatural — and at how nature, certainly, eventually, awesomely, will prove that in the most devastating way possible.