All the victims are mothers and small children, Assistant Fire Chief Kevin Barlow said. The youngest child was about 4 years old.
The flooding ravaged a community that straddles the border from Hildale, Utah, to Colorado City, Arizona.
Most of the people who live in the community are members of the Warren Jeffs polygamist sect known as the Fundamentalist Church of Jesus Christ of Latter-day Saints (FLDS).
The flash flood started with heavy rains Monday evening in the canyons above Hildale, Barlow said. The rush of water was so intense it washed two vehicles several hundred yards downstream.
