Mountain and desert areas could get 5 to 10 inches of (12 to 25 cm) rain, as much as the deserts typically see in a year, forecasters said. The first tropical storm to pelt Los Angeles County since 1939 triggered serious flooding in the San Gabriel Mountains east of the city and coastal areas to the northwest in Ventura County. San Bernardino County ordered evacuations of a number of towns in the mountains and valleys where social media images showed torrents of water, mud, rock and trees.