TO THE RODOLPH brothers of Casper, the Leg Lake Cirque was known as the China Wall. They'd visited the rim several times before, coming up the back way, a steep but tolerable hike through neighboring Upper Silas Canyon. Aaron, 28, had backpacked in the area for a week at a time, and Luke, 23, had hiked the entire canyon rim by himself.

A large party of Rodolphs had made a three-hour drive from Casper to the canyon trailhead on Thursday, the night before Absolon and Herlihy left Lander. The group included Aaron, Luke, and their older brother, Isaiah; Eli Rodolph, a cousin from South Dakota; Eric McDonald, a family friend; and wives and girlfriends—eight adults in all, plus Isaiah's four children. They set up camp at a no-name lake and spent Friday fishing and hiking. On Saturday, Luke and Aaron decided to take Eli and Eric to the China Wall.

Although the trail up the canyon ends at Island Lake, the four kept going, to the towering headwall of the cirque. They all walked to the rim, which offered a panoramic view of the basin, the surrounding peaks, and Lander in the distance. It was a favorite spot that neither Aaron nor Luke had seen for a while. Aaron had been building a landscaping business in Casper, while Luke had spent four years in the U.S. Army's 82nd Airborne Division, including two tours in Iraq, before coming home to work with his brother.

They saw no one after leaving the trail. They spent half an hour on the rim, soaking up the scenery and tossing rocks down toward Leg Lake. Later, Aaron would estimate that the group had pushed four or five small boulders over the cliff. "It was really awesome to watch the rocks fall," he recalled. "You could see every bounce, every hit, all the way to the glacier."

Around five, the Rodolph party decided to make their way to a new spot a quarter-mile away, where the rim becomes a series of jagged overhangs above the basin—a good place to watch rocks fall, they figured. Luke led the way to a 15-foot promontory jutting into space. He went out a few feet, peered over the right edge, picked up a bowling-ball-size hunk of granite, and launched it into the void. Then he crouched down and leaned farther over the edge to watch its descent.

His new position gave him an unimpeded view of the area below. He saw, to his surprise, two men in white helmets 200 feet beneath him. And at the same moment he registered their presence, the plummeting rock struck one of the men directly on the head.