About 2,500 people were stranded after thunderstorms caused mountain mudslides in Southern California, while one person was found dead in a flooded creek Sunday, authorities said.
The mudslides swallowed cars, campers and vans.
One person was killed after swift-moving floods swept their car away, authorities said.
The stranded included 500 children and adults who had arrived at a Forest Falls, California, campground Sunday morning.
"Our concern is that they're isolated at that campground and no longer have access out of the mountain," San Bernardino County Fire spokesman Kyle Hauducoeur said.
The debris flow engulfed one home. Emergency crews rescued the home's resident.
"The rain in this area, at times, was the equivalent of what you would see from a major hurricane," Hauducoeur said.
The storm moved in quickly, snapping trees and sending a torrent of water rushing through the region. In Forest Falls, a wall of mud as high as 15 feet and up to 75 feet wide was reported.
In Mount Baldy, rescuers broke the windows of a car trapped underwater, making sure no one was inside. The vehicle was empty, a small shred of hope amid the devastation witnessed by residents such as Michael Scully.
"This is the worst we've had since at least 1969," Scully said.
Monsoonal moisture brought brief but fierce storms to mountain, desert and inland areas. In and around Palm Springs, knee-deep water flooded city streets and stranded vehicles. In the city of Redlands, the storm downed a tree and knocked out power to a few neighborhoods.
Authorities made reverse 911 calls to urge residents to stay put while crews cleared the roads with bulldozers.
All the water was desperately needed elsewhere in the state. In northern and central California, firefighters battled more than a dozen fires. Crews created a six-mile fire line to protect the town of Burney.
"I have a lot of confidence in our brothers and sisters that we'll all come out of this OK," Burney Fire Department Chief Ray Barber said.
ABC News Radio and the Associated Press contributed to this report.