A winter storm on Saturday morning forced the closure of Interstate 5 over the Grapevine at Tejon Pass, temporarily blocking California's main north-south artery.
The heavily traveled stretch of freeway was shut down shortly before 10 a.m. because of snow and ice, making the steep grade difficult to navigate, officials said.
It's unknown when the road will be reopened.
"That's up to Mother Nature," said California Highway Patrol Officer Eric Priessman said.
Caltrans and the California Highway Patrol shut down the northbound I-5 at Parker Road in Castaic, along with Highway 58 through the Tehachapi Pass, because of icy conditons, Priessman said.
The Tejon Pass is a particularly vulnerable area because of its steep hills and the number of big-rigs that travel on it, officials said.
Motorists are urged to use Highway 101 to get to and from Los Angeles County. Another alternate route is Highway 126 west to the 101 north through Ventura County, Pressman said.