Heavy thunderstorms developed in mountains near the Mountain High Ski Area at midday Saturday, and the National Weather Service issued Flash Flood Warnings.
Rain was falling at the rate of 1.7 inches per hour in Big Pines and Wrightwood in Los Angeles County, and nearby Phelan, Llano and Pinon Hills in San Bernardino County, according to National Weather Service Doppler radars.
At 12:40 p.m., forecasters in Oxnard and San Diego activated Emergency Alert System alarms as forecasters said water would rise in arrotos and canyons from Big Pine east as far as Cajon Pass.
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Flash flooding was held to be likely on Big Pines Highway, state routes 2 and 138, and secondary roads in the area north and west of Cajon Pass.