TONTO NATIONAL FOREST, Ariz.  — The flash flood that killed nine people in an Arizona canyon began its deadly descent as an impressive but avoidable surge of churning water, black with cinders from a recent wildfire and choked with tumbling tree trunks and limbs.

By the time it reached a rocky swimming hole several miles downstream, it was a roaring torrent 6 feet high, and an extended family celebrating a birthday while seeking refuge from the summer heat had no warning — and no chance to escape.

The bodies were found up to 2 miles away. Five other people were rescued, some of them clinging desperately to trees, and were treated for hypothermia and released.

As rescuers searched Monday for a 27-year-old man still missing about 100 miles (160 kilometers) northeast of Phoenix, authorities identified the victims, who ranged in age from 2 to 60.

Among them were three generations of a family. Five of the dead were children.

The victims had been lounging Saturday in the Water Wheel swimming hole, where the river narrows and rocks create pools and a series of small waterfalls. The narrowing of the canyon squeezed the flow of water and helped give it deadly force.

The river roared to life after a thunderstorm had dumped up to 1½ inches of rain in an hour, prompting a flash flood warning from the National Weather Service.

But there is little or no cellphone service in the remote area, and without a weather radio, the swimmers would have been unaware.

“They had no warning. They heard a roar, and it was on top of them,” said Fire Chief Ron Sattelmaier of the Water Wheel Fire and Medical District.

Carrie Templin, a spokesman for the Tonto National Forest, said people headed to the forest should check weather alerts ahead of time to determine whether it’s safe. It is hard to predict where rain will fall in the desert Southwest, and people should know that heavy downfalls can cause flash flooding, Templin said.

“How do you warn people about Mother Nature?” Templin asked.

About 40 volunteer workers and four search dogs looked for the missing man.

About five miles up the mountain, where a June wildfire scorched 11 square miles of the Tonto National Forest, Scott Muller first spotted the water rumbling down the nearly dry East Verde River. He was spending the day with a dozen other members of AZ Krawlers, a volunteer group of Jeep owners that was checking roads and trails for dangerous erosion and missing signs.

He began making a video with his phone and comfortably scampered to the bank before water clogged with debris whooshed past.

“We had no idea how fast and big it was going to be,” Muller said.

In a wildfire area, the scorched land repels water, making flooding worse.

Muller and the others got in their vehicles and rushed down the mountain on an unpaved fire control road to get another look. Emerging onto a paved road, they drove up the mountain to a bridge that was below where the waters would sweep through the swimming hole.