Authorities in Utah say the death toll is now up to a dozen after flash floods along the Utah-Arizona border Monday engulfed two vehicles carrying 16 people, and swept them into a waterway that is normally dry.
One person from those vehicles remains missing.
"This is one of the worst weather-related disasters in the history of the state of Utah and because of that we are bringing the full resources of the state to bear," said Spencer Cox, the state's lieutenant governor.
Updated at 10:35 p.m. ET: fourth hiker's body recovered
In a separate incident, officials say four people are dead and three are missing after heavy rains caused flash floods to rush through sections of Zion National Park.
The Associated Press reports that park spokeswoman Holly Baker said a group of three women and four men set off Monday before the park closed slot canyons because of heavy rains and flood warnings.
"Park rangers advised the group when they picked up their permit Monday that weather conditions were poor and flooding was likely, but until canyons are closed, Baker said rangers leave it up to visitors to determine whether it's safe to continue their excursions.
The park doesn't close canyons until actual flooding occurs, which was around 5 p.m. Monday, [Baker] said."
The Zion group was reportedly canyoneering in a narrow and short slot canyon called Keyhole.
According to a statement by the National Park Service, storms arrived at Zion National Park and dropped 0.63 of an inch of water in an hour.
"Rangers received a report of a group of seven individuals canyoneering in Keyhole Canyon shortly before the flooding began. Their unoccupied vehicles were located on Monday evening and a search began the morning of Tuesday, September 15, 2015 when it was determined that these individuals had not exited the canyon.
"Of the seven individuals involved, three fatalities are confirmed and the remaining four are missing. Names are not being released at this time, pending notification of kin. As the search continues for the missing hikers, high water levels and continued rain showers pose further flash flooding concerns and have hampered searchers' access to the technical portions of the canyoneering route."
NPR's Howard Berkes reports from Salt Lake City:
"Ropes, rappelling and swimming are required to navigate the tight canyon. The hikers never returned to their cars. Twenty miles away, in the polygamous community of Hildale, an SUV and van carrying 16 women and children were swept away by one of the biggest flashfloods locals had ever seen.
"New flood warnings were issued Tuesday evening. Heavy rain falling miles away flows into dry washes and narrow canyons and builds in intensity, often catching victims by surprise."
The National Weather Service has issued a flash flood warning Tuesday evening complicating efforts for search crews.
In Hildale, Utah, along the Arizona border, crews resumed their search Tuesday on the banks of Short Creek. They used dogs to search for the missing, and heavy equipment to clear tons of mud and debris.
The Facebook page for Utah's Washington County, which has been providing updates on the search mission, states:
"The creek is still running high and the area is unstable with large volumes of mud and debris. Please stay away from the area and allow searchers to continue their efforts."
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Three victims survived, and one was transported to a hospital Monday.
Search and rescue efforts were scaled back overnight due to the treacherous conditions. Emergency responders from the towns of Hildale, Colorado City, Hurricane and from the Washington County Sheriff's office, along with search and rescue workers from Mohave County, Ariz and Apple Valley, Utah were on the scene Monday night.
"We're pretty used to flash flooding, but this is significantly more than what we're used to," said Hildale Assistant Fire Chief Kevin Barlow.
The Utah Division of Emergency Management said in a statement that the streets in flood-affected areas were awash in mud, sand, boulders and debris, and that many homes were without power and water.
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