National Geographic : 1960 Mar
JOHN R. STACY, U. S. GEOLOGICALSURVEY (ABOVE) AND WILLIAMB. HALL Shattered by the Quake, State Highway 287 Disappears Into Hebgen Lake Its bed warped, the lake today drowns part of the north shore under nine feet of water and exposes its southeast rim. Four big landslips cut the road. Cadillac plunges off a zigzag crack across U. S. 191. Alarmed by the quake, the driver and his family were fleeing for West Yellowstone when the car turned turtle. The occupants crawled out of the hole where the windshield had been. sumed lost beneath hundreds of feet of rock. "That south wall of the canyon must have been on trigger edge for years," Dr. Jarvis B. Hadley of the U. S. Geological Survey told me-"a mountain slide simply waiting for an earthquake to happen." Dr. Hadley was one of more than 25 geol ogists, geophysicists, ground-water experts, and other scientists assigned by the Survey to study the earthquake area. He had felt the quake himself; on the night of the slide he was in the town of Ennis, 45 miles downstream. 336 "Rock layers in the mountain face tilted steeply toward the river," the geologist ex plained. "They were weathered and cracked, relatively soft schists and gneiss mixed with slippery mica, with clay in the old clefts and cracks. These greased the skids when the face came down. "At the base of the ridge ran a buttress of marblelike dolomite. This ledge broke cleanly, probably in the first quake. It had been holding up the mountain." The layers above snapped, shifted slightly, much as sheets of glass stacked together might move, then hesitated.