A helicopter rescued hikers clinging to tree branches and perched on boulders as a flash flood tore through a normally quiet creek in Arizona, where unpredictable summer storms can rapidly wash churning torrents into canyons and trap those looking to take advantage of cooler weather after the rain.

Seventeen hikers, including a young child, were stranded on Monday in a scenic canyon on the outskirts of Tucson, just over a week after floodwaters killed 10 members of an extended family more than 225km to the north.

In southern Arizona, two final hikers were lifted to safety yesterday from Tanque Verde Falls after they spent the night stuck on the side of a cliff in a rocky, narrow canyon, authorities said.

The rescue was a reminder of the dangers of flash flooding during Arizona's monsoon, a weather phenomenon that brings powerful and unpredictable storms each summer with bursts of heavy rain that can quickly overwhelm usually calm waterways. On July 15, a family celebrating a birthday at a swimming hole in central Arizona were swept away by a wall of water that cascaded down a canyon without warning after a storm.


After those deaths, rescuers considered the hikers who were plucked to safety on Monday very lucky. Erick Maldonado, who supervises the sheriff's search-and-rescue unit, said he understands families come to outdoor swimming spots to cool off, but it has to be done responsibly.

"There were generations of a family that were literally swept away, and that easily could've happened yesterday," he said.

The creek normally has just a trickle of water, allowing people to play in shallow pools, but the water level jumped about tenfold in five minutes and was at least 2m to 3m deep.