PHOENIX (AP) -- Desert communities in Arizona and California were cleaning up Friday after summer storms unleashed muddy torrents into roadways and toppled huge trees into homes and vehicles.
A man in Los Angeles County was hoisted to safety by a helicopter when his pickup truck was surrounded by a river of muddy water.
Residents of the Phoenix metro area surveyed damage in their neighborhoods after high winds and heavy downbursts of rain downed scores of huge, old trees Thursday evening.
Jesse Thomas of All About Trees said Friday the phone at his Phoenix tree-removal service was ringing non-stop. He spoke as his crew dealt with an 80-foot tall (24-meter), 20-ton Aleppo pine that crashed into a house from a neighboring property.
"It's been a few years since we have seen a tree this big come down," Thomas said.
In Las Vegas, officials on Friday said seven people had to be rescued and another one was still missing after they were swept away by rushing flood waters in two washes.
Clark County Fire Department deputy chief Jeff Buchanan said emergency personnel were still searching for the person who went missing in a wash where another one was rescued and then transported to a hospital. He said six people were also rescued from a wash behind the Linq casino-hotel on the Las Vegas Strip.
The summer storms in the U.S. Southwest are known as monsoons, a term many associate with the Indian subcontinent and the Bay of Bengal.
A monsoon is simply a reversal of winds, National Weather Service forecaster Travis Wilson said. In the American Southwest, that means a switch of the region's wintertime westerly winds for the summertime's southerly and southeasterly flow bringing in moisture from Mexico's Gulf of California.
"With all that heat in the summer, and the clear skies, the moisture gets lifted up into the atmosphere and then we get thunderstorms and a lot of rain," said Wilson. "A lot of wind, too."
In the Phoenix area, the storms flooded streets, delayed flights and temporarily knocked out power to thousands of people. Dozens of utility company workers on Friday were replacing broken power poles and repairing downed lines.
Rainfall amounts from Thursday evening included 1.81 inches (4.59 cm) at a city park in east Phoenix, 1.74 inch (4.42 cm) near the border between Phoenix and Scottsdale, and 1.69 inches (4.29 cm) along the Salt River near the border between Phoenix and Tempe, the National Weather Service said.
The rainfall average for Phoenix is about 1 inch (2.54 cm) for July and August combined, Wilson said.
A tornado formed briefly during the storms in Phoenix but apparently didn't cause any damage other than kicking up dust, the National Weather Service said.
The Phoenix Zoo was closed Friday as crews cleaned up uprooted trees, damaged structures and flooded trails. All the animals were safe and accounted for and no animal habitats were harmed, Zoo spokeswoman Linda Hardwick said.
"It was definitely a good storm that hit," Hardwick said. "A lot of these trees can't be replaced ... It's unfortunate, because the more shade we have here at the zoo, the better, just because of the extreme temperatures."
Jim Phipps, a municipal worker who lives in the Phoenix suburb of Tempe, had difficulty getting home Thursday evening. "Two of the three access points to my little cul-de-sac were blocked" by downed trees and flooding, Phipps said. He had to use a winch to remove a downed olive tree blocking his driveway, he said.
The semi-rural Southern California desert community of Acton north of Los Angeles was also mopping up Friday after huge thunderheads caused by monsoon conditions unleashed muddy torrents through streets and homes, threatened a commuter rail line and forced rescues of trapped motorists.
Fourteen people in that area were rescued by fire crews, including the man who was trapped in a truck, the Los Angeles County Fire Department said.
The Metrolink commuter train reported cancellations and delays during the Friday morning rush hour. One of its trains on a run between Los Angeles and the high desert Antelope Valley was forced to stop Thursday as rushing water chewed away at an earthen embankment underneath the tracks.