HILDALE, Utah — Rescuers trudged through muddy streambeds Tuesday in a small polygamous town on the Utah-Arizona border and found the bodies of several children who died when their two vehicles were swept away in a torrent of floodwaters that killed at least 12 people. The same flash floods claimed at least four lives in nearby Zion National Park.

The van and SUV were filled with three women and 13 children when a wall of brown water overtook them Monday evening, carrying the vehicles several hundred yards downstream and sending them plunging down a flooded-out embankment with terrifying force. The SUV was smashed beyond recognition. Three people survived, all of them children, in the secluded community that is the home base of Warren Jeffs’ polygamous sect.

A witness described rushing to where the vehicles came to a stop and seeing a gruesome scene of body parts, twisted metal and a young boy who survived the flood.

“The little boy was standing there,” Yvonne Holm said. “He said, ‘Are you guys going to help me?’”

Only one person was still missing Tuesday in the border town, and authorities had not identified the dead. The children in the vehicles ranged from 4 years old to teenagers.

At nearby Zion National Park, authorities found four bodies and searched for three missing hikers who set out Monday to rappel down a narrow slot canyon. They left before park officials closed the canyons that evening because of flood warnings, park spokeswoman Holly Baker said. The hikers, from California and Nevada, were all in their 40s and 50s, Baker said. She had no details on their identities.

In Hildale, the streets were caked in red mud, and earth movers cleared the roads and piled up mounds of dirt. As a helicopter buzzed overhead, crowds of boys in jeans and girls and women wearing deep-colored prairie dresses watched the rescue effort.

Residents called it the worst flood in memory for the sister towns of Hildale, Utah, and Colorado City, Arizona, located about 315 miles south of Salt Lake City at the foot of picturesque red rock cliffs.