In a large area of the Southwestern U.S. desert on Monday, workers raced to remove mud from roads and buildings as the first tropical storm to hit Southern California in 84 years traveled north, triggering flood warnings in half a dozen states.

Although Tropical Storm Hilary had diminished in strength when it approached the Rocky Mountains, the National Hurricane Center in Miami issued a warning that "continued life-threatening and locally catastrophic flooding" was anticipated in some areas of the region.

According to weather experts, the risk for flooding in states further north on Monday was greatest across much of southeastern Oregon and into the west-central highlands of Idaho, with probable thunderstorms and localized torrential showers on Tuesday.

A boil-water order was issued for around 400 houses in the Mount Charleston area, where the only road in and out was washed out, as Hilary proceeded eastward into the adjacent state of Nevada. Flooding was also recorded. The area is about 40 miles (64 km) west of Las Vegas.

Prior to transitioning into a tropical storm, Hurricane Hilary originally hit Mexico's dry Baja California Peninsula as a hurricane, resulting in severe flooding and one fatality. No fatalities, severe injuries, or severe property damage have yet been reported in California, but officials have warned that risks still exist, particularly in hilly areas where wet hillsides might cause mudslides.

Since they often are modest and remain deep in the tropics, it is unusual for an Eastern Pacific storm to be this huge, according to Kristen Corbosiero, an atmospheric scientist at the University of Albany who specializes in Pacific storms.

Both hot air and hot water were essential for Hilary's quick expansion, guiding it on an unusual but not entirely unprecedented course that dropped rain in some typically arid regions.

About 400 people were left without a place to stay after Death Valley National Park was forced to close indefinitely due to Hilary, who also broke daily rainfall records in San Diego. Until the roads could be made passable, the people in the park was sheltering at Furnace Creek, Stovepipe Wells, and Panamint Springs.

(With input from AP)

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