It looked like a scene out of the movie Twister.
The storms, described as a once-in-a-decade event, were the result of a dramatic difference in pressure between a strong, high-pressure system and a cold, low-pressure system, meteorologists said. This funnels strong winds down mountain canyons and slopes.
The system brought high wind warnings and advisories for California, Utah, Nevada, Wyoming, Arizona and New Mexico. The blustery weather is expected to eventually hit Oklahoma, Missouri and Indiana.
In Southern California, the storm knocked out electricity to more than 350,000 utility customers. By early Friday, 270,000 of them were still without power.
A state of emergency was declared in Los Angeles County, where schools in a dozen communities were closed.
In some neighborhoods, concrete light poles cracked in half. Darkened traffic signals and fallen palm tree fronds and branches snarled traffic. At a Shell station, the roof collapsed into a heap of twisted metal.
In heavily damaged Pasadena, schools and libraries closed and a local emergency, the first since 2004, was declared. Officials said 40 people were evacuated from an apartment building after a tree smashed part of the roof.
Pasadena is known for its historic homes and wide oak-lined streets that are frequently depicted in films.
Many residents Thursday blamed the city for protecting its old trees from over-trimming to such an extent that they have now become a public safety hazard.
It's a fast moving weather system and is moving out of the area quickly.