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Idaho has had one of the most convulsive recent geologic histories of any state. Only a few million years ago, it was an almost continuous cataclysm of volcanic eruptions, earthquakes, and lava flows. The Yellowstone plateau, two hundred miles off to the northwest, still exhibits the remnants of such activity, as do the Cascade Ranges to the West. (In the fall of 1983, one of the biggest earthquakes in recent U.S. history struck a remote part of Idaho less than two hundred miles from the Teton site.) The whole eastern Snake River Plain, including the Teton site, is a vast bed of basaltic rock. The hazards of building a dam in such terrain, however, became an issue almost entirely by accident. In 1973, Robert Curry was teaching geology at the University of Montana; he did some occasional consulting work for the Sierra Club, mostly on the effects of logging and mining operations. Though he was quite familiar with the geological firmament of southern Idaho, and knew it was anything but firm, he always assumed the Bureau knew how to build a safe dam in such a locale. He also assumed it would have the sense not to build one at an absolutely terrible site. “The first time I heard anyone question the safety of Teton Dam,” Curry remembers, “is when some people with the Idaho Environmental Council called me up in 1973. They had been sitting around drinking beer with some guys from the Geologic Survey and one of the Survey guys said—I guess he didn’t even mean to let it out—‘Well, the Bureau’s going to have a hell of a time building Teton Dam.’ An IEC member asked him what he meant, and the Survey guy said, ‘Well, it’s really a crummy spot to put a dam.’ I was one of the few geologists around who had much sympathy for the environmental side, so they called me up and asked me what I knew. I didn’t know anything. I figured, well, they’d built American Falls Dam down there and some other ones, so they must know what they’re doing. But I asked the Survey if I could see their cross section anyway. I looked at it and that’s when I said, ‘Holy Christ!’

“The stuff they were going to build the dam on—all those ashflows and rhyolitic rock—may look solid to you, but it’s really a veneer, sort of like the wood veneer on a cheap desk. It’s brittle, it’s cracked. It could peel off just like the veneer on the desk. They were going to scrape away the worst of it and then say that they were anchoring the dam in bedrock. But it isn’t really what most geologists would call bedrock. The dam was not going to have a true bedrock foundation.

“It was such an obviously lousy site to a trained geologist,” Curry added, “it makes you wonder what happens to human judgment inside a bureaucracy.”

Accompanying the Geologic Survey’s schematic of the Teton foundation was a report to the Bureau of Reclamation written by four geologists in its regional office, which—in its first version—raised “certain questions about the fundamental safety of the Teton Dam.... Despite the incompleteness of the data,” the geologists cautioned, “we fell obliged to bring them to your attention now, while they may still be useful and on the chance that some factors may not have been adequately considered in design of the project.”

From reading the memorandum, it was clear that the four geologists considered the possibility of an earthquake to be the greatest hazard associated with the dam. “Young ashflows and associated rhyolitic volcanics like those being used as buttresses for the dam,” they wrote, “are cut by very young block faults.” Often, they said, undetected faults with substantial destructive capability can exist in such terrain. “The Seismic Risk Map of the coterminous United States assigns southeastern Idaho to Zone 3,” the code for highest seismic risk. Although the geologists—Steven Oriel, Hal Prostka, Ed Ruppel, and David Schleicher—stopped just short of urging the Bureau to abandon its plans to build on the Teton site, they asked that their observations “be given the serious consideration we believe