Several overturned semis on a Utah highway. Hundreds of thousands without power in California. A wind gust reaching 123-mph in Colorado.

The powerful winds that tore across Western states Thursday created a path of destruction that closed schools, left neighborhoods with a snarl of downed trees and power lines, and prompted some communities to declare emergencies.

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.