(CNN) -- As floodwater raged around their pickup, the family of a 6-year-old Arizona boy escaped to higher ground. The boy, however, was swept away. Teams were looking for his body on Friday, the Yavapai County Sheriff's Office said.
Meanwhile, an evacuation order for some Los Angeles, California, residents was lifted, and the mayor said those people can safely return home
Authorities were classifying the Arizona operation as a recovery, presuming that a child could not survive in the raging water, the office said in a news release. The boy's name was not released.
Rain has hindered attempts to find the boy after the incident Thursday night, authorities said.
"This effort continued through the night without success. Because of low visibility, along with the wind and rain, DPS (Department of Public Safety) Ranger helicopter was unable to fly over the area," the sheriff's office said.
The family's pickup got stuck near the northern community of Mayer, between Flagstaff and Phoenix in central Arizona.
On Friday, the vehicle sat alone in a vast sea of mud, which reached nearly to the bottom of the windows and partially filled the area under the crumpled hood. The vehicle was tilted forward, as if diving into the muddy soup.
According to a preliminary report, the boy was in the pickup with his 8-year-old sister and parents, who were trying to take him to a hospital when floodwater swept the pickup off the road.
The mother was able to reach higher ground, and the father took the children to the bed of the vehicle for safety. By the time firefighters reached the scene, rising water had pushed the three from the bed. The father was able to reach a safe area with his daughter but the son was missing.
The flooding was the result of heavy rainstorms that started pounding parts of neighboring California on Monday and continued through the week. Upper elevations got heavy snow.
Conditions in the area were not likely to improve until Saturday afternoon, the National Weather Service said. Forecasters predicted continued flooding of many rivers and streams and up to an additional foot of snow in the mountains.
In Los Angeles, Mayor Antonio Villaraigosa said Friday that the 2,000 city residents who were evacuated because of the storms could return. The permission came after teams of geologists and structural experts determined that areas threatened by mudslides were safe enough, he said at a news conference.
Last year's wildfires burned trees and vegetation that normally hold soil in place and prevent hillsides from collapsing.
Hundreds of residents also had been evacuated in Los Angeles County, and many of these were cleared to return home, according to the Coordinated Agency Recovery Effort's Web site.
The storms stem from El Nino, a warm ocean current from the South Pacific, meteorologists said.
CNN's Sean Morris contributed to this report.