The storm Wednesday and early Thursday also dumped snow on rain on much of southern California and parts of Nevada outside Las Vegas.
The National Weather Service measured 3.6 inches of snow overnight at Las Vegas' McCarran International Airport, and meteorologist Jerome Jacques said about 2 inches was left before dawn on the ground near the "Welcome to Fabulous Las Vegas" sign.
"Snow is not unknown in the Las Vegas valley. On average we get 1/2 inch of snow a year," Jacques said. "But this amount made it a significant storm. We haven't had this amount of snow since 1979."
The weather service recorded 7.5 inches of snow at McCarran on Jan. 30-31, 1979.
The snow Wednesday prompted the cancellation of all flights in and out of Vegas. Visitors parked and posed for pictures wearing hooded jackets.
Other parts of Nevada were forecast to receive as much as 8 inches of snow in the second winter storm this week to drop snow on the desert city. Snowfall is common in nearby mountains hills, but not on the Strip or surrounding neighborhoods.
Elsewhere, snow shut Interstate 15 over 4,190-foot Cajon Pass east of Los Angeles. By early Thursday, just a single lane on the southbound side was open, as officers escorted a small stream of drivers through the pass.
Interstate 5, a major trucking and travel route connecting Southern California with the Central Valley and Northern California was shut down over 4,144-foot Tejon Pass, and roads through the San Gabriel Mountains connecting metropolitan Los Angeles to the commuter suburbs of Palmdale and Lancaster in the high desert to the north also were closed.
An overflowing river on the U.S.-Mexico border Wednesday led to the evacuation of nearly two dozen people and rescues of about 50 horses.
Snow also fell across much of Washington state on Wednesday, with Spokane, in the northeast part of the state, declaring a snow emergency and vowing that its snowplows would be working nonstop until the streets were clear.
Most areas of Spokane had picked up 8 inches of snow by evening, with another 5-10 inches expected by daybreak Thursday, said National Weather Service meteorologist Jeffrey Cote.
Massive backups developed below all the passes, which authorities hope to have reopened Thursday.
The storm dumped as much as 4 feet of snow at Big Bear in the San Bernardino Mountains, said James Oh, a forecaster with the National Weather Service in San Diego.
Schools were closed Thursday, many of them for the fourth straight day, in several high desert and mountain districts.
And soldiers at Fort Irwin near Barstow were unable to deploy to Iraq Wednesday as planned because of the snowy conditions.
Calen Weiss, 19, of Tarzana, his brother and two friends wanted to go snowboarding at Big Bear but instead got stuck on I-15 in Cajon Pass for an hour as visibility fell to about 40 yards.
"It looks like Whoville, all snowy, but with less joy and more extreme misery," he said by phone from the Summit Inn.
Heavy rain also fell in some parts of Southern California through the day.
Near the California-Mexico border, San Diego firefighters and lifeguards evacuated 21 people along the overflowing Tijuana River, said spokesman Maurice Luque. They included 12 to 15 people who were on high ground outside a home, surrounded by up to 4 feet of water.
Five people were taken out by helicopter, while others were escorted in Border Patrol all-terrain vehicles, Luque said. Three men were taken to a hospital for treatment of hypothermia.
About 50 horses also were evacuated, but three others drowned and one was euthanized after tripping on barbed wire, Luque said.
In the Santa Clarita area north of Los Angeles, a wind gust caused a helicopter to crash, killing an electrical worker on the ground and leaving the pilot with minor injuries, county fire Inspector Frank Garrido said.
Even Malibu got a dusting of snow, as the usually balmy city saw a half-inch in the afternoon.
"It's kind of cool if you think about it, said Craig Levy, director of a juvenile detention camp. "It's kind of unusual to see snow in Malibu."
Associated Press Writers Solvej Schou and Daisy Nguyen in Los Angeles and Elliot Spagat in San Diego contributed to this report.