Story highlights Residents are asked to boil water due to the risk of contamination

In one incident, at least four people killed while canyoneering; three are missing

Most in the community are members of the Warren Jeffs polygamist sect

(CNN) Two vehicles carrying women and children from a park were washed away by a flash flood barreling down a canyon near the Utah-Arizona border, leaving 12 people dead and one person missing, officials said Tuesday.

It was not the only deadly incident attributable to the fast-moving water. In Zion National Park's Keyhole Canyon, four people who were canyoneering were killed and three are missing, National Park Service officials said.

At least six children and three women died in the vehicles that were swept away in the border area, according to Utah officials in the city of Hildale and with Washington County Emergency Services.

Three people survived Monday's flood, including a boy who was found walking around a creek, said Hildale Mayor Philip Barlow.

Two survived by escaping from their vehicle, he said. The youngest fatality was a child about age 4, said Hildale Assistant Fire Chief Kevin Barlow.

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