The Chinese group took the earlier session and then left by bus around 2 p.m. along the long, winding road back to Chengdu. “That’s what is upsetting,” said Teri Kopp of Seattle, who sobbed quietly as she recounted that morning. “We don’t know what happened to that busload of people.”

The Americans were gathering for a lecture at the reserve’s panda breeding center when they noticed strange behavior by the animals. The birds that had been chirping in the bushes, or twirling in the skies overhead, were gone. There was almost no sound. The pandas seemed nervous. Then at 2:28, the earthquake hit.

“For me, what was terrifying was when the top of the cliffs started exploding,” Ms. Kopp said. “All the boulders started coming down. The staff at the reserve was wonderful. They were yelling at us to get under some structure.”

The steep mountains looming over the breeding center were collapsing in landslides as strong aftershocks rippled through the valley. “These rocks were just flying in the air,” Mr. Weber said. “A few of the rocks were the size of Volkswagens.”

The aftershocks finally halted, and the people at the reserve soon realized they were trapped. Boulders blocked the path leading to a bridge that linked the breeding center to the road to Wolong village. A new path was needed: The Frenchman, three Americans, a tour guide and the panda keepers created a route by climbing over cages, stepping carefully along the top of a wall high above a river and rigging a ladder up to the bridge. It was a precarious, rain-slicked solution.

One by one, everyone carefully moved forward. One of the Americans was a 79-year-old Californian traveling with a friend. “It was very scary,” Ms. Capito said. When the last person had made it to the bridge and out to the road, the staff raced back for the baby pandas. They carried the cubs tucked under their arms as they slowly edged forward above the river and then up the ladder.

All 13 cubs were saved. They were put inside a small ticket booth, a home that kept them from escaping, if not happy. “You could hear them,” Ms. Capito said. “They were just tearing the place apart. And when they let them out, they would just romp and play. Not one got killed. I couldn’t believe it.”