From CNN.com:

Heavy snow kept a mountain stretch of Interstate 5 closed Thursday, as several hundred vehicles were stranded south of Bakersfield to north of Santa Clarita, the California Highway Patrol said.

I’ve driven this pass, also known as The Grapevine, and it’s hairy even under good conditions. This happens every once in a while, and because they’re not equiped to deal with this sort of thing, the traffic grinds to a halt for hours (I’ve been stuck there for hours due to severe fog in the central valley!).