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Swift water rescue teams were responding to several vehicles being swept down a river of high-rising floodwaters at La Paz and Pebble Beach drives, according to fire officials.
Upon arrival, rescue teams discovered one car under water and found the body of a person inside. It was not yet clear how the person died.
The Inland Empire was hit with heavy rain, causing raging waters to turn into mudflow along Highway 138 in the West Cajon Valley.
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The highway was shut down in both directions at Lone Pine Road until further notice, fire officials said. The road between the 15 Freeway and State Route 2 was declared impassable with over 2 feet of mud flooding the highway.