Story highlights Northbound lanes of Interstate 5 in Tehachapi Mountains are reopened Friday afternoon

"Some cars got really messed up by huge boulders," motorist says

Nick Zernick spends 20 hours on highway when travel should have taken only seven hours

Los Angeles (CNN) After scrambling to rescue motorists stranded on roadways as flash floods and large hail pounded areas north of Los Angeles, Southern California authorities began digging out Friday.

Flash floods sent water flowing into roads Thursday, triggering mudslides that forced the closure of a portion of Interstate 5 in the Tehachapi Mountains, a highway known locally as "the grapevine." California Highway Patrol said Friday night that I-5 had reopened after a cleanup.

On Friday afternoon, the northbound portion of the highway was reopened after street sweepers scoured mud from the road, the California Department of Transportation said on Twitter.

The southbound lanes, however, were still caked with mud, with clogged drains, on Friday afternoon, Caltrans said.

#I5Mudslide NB5 expected to open early afternoon today. SB5 1 lane open by late afternoon. Rain could delay opening. pic.twitter.com/PKiPoUy6ZK — Caltrans District 7 (@CaltransDist7) October 16, 2015

Some motorists fled on Thursday, while others sat trapped in cars and called 911 for help, according to Lisa Williams of the Los Angeles County Emergency Management.

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