At that moment, "there were no tents, there were no picnic tables, there were no coolers," Cashin said. "It was all gone, and it was strewn down the river."
A few hours earlier, a father in the group awoke as water pooled around his tent and others. He and the rest of the group huddled in pajamas and socks on a higher ledge as they waited in the rain for emergency crews.
Rescuers brought the family to safety within about a half an hour, Cashin said, working quickly because they feared another flood would rush down the slot canyon.
Crews brought the group to a St. George hotel, where Red Cross workers gave them food and dry clothing. The youngest in the group was 9. The oldest person was 57, police said.
At least one man in the family and some officers later returned to the canyon to try to retrieve one of the cars. They searched for a lost backpack with keys to the vehicles but could not find it, Cashin said.
The family had arrived at the campsite a day in advance of a larger scheduled family reunion. Most of the people rescued have returned to Las Vegas.
Authorities say summer rains often send water rushing over slick rock and sand in the backcountry canyons near Zion National Park. They warn campers to check weather forecasts often and keep an eye out for storm clouds.