JACKSON, Wyo. (AP) — Simeon Caskey stood beneath the steep, boulder-strewn slope that looms over Hidden Falls, pointing out a rock wall with an ominous crack a few hundred feet (91 meters) overhead.

The Grand Teton National Park ranger, who leads the park's physical sciences branch, was in an area that's been closed to the public — and he was explaining why. If the buttress were to fail, he said, chunks of it might tear through the base of the 100-foot (30.5-meter) cascade where visitors often crowd to photograph and enjoy the falls.

"It seems like a good chance that at least a percent of it w...