Snow in California is not exactly news breaking, given that here are a plethora of areas in California...that get copious amounts of snow.
Which is the reason that there are so many ski resorts in the state.
California Ski Resort Map
The worst conditions I've ever driven in, was going over Donner Pass during the Blizzard of 1988 in almost a complete whiteout, whereby I-80 had been reduced from four lanes...to just one. Not even the plows were out at this point.
I eventually had a string of cars following me at my speed of 5-10 mph, that even when I pulled over every so often to let hopefully someone else lead, they would pull over behind me...and wait for me to get going again.
The only way I could tell that I was on the main path of the four lane Interstate, is because the rental car would start having snow come over the hood...if I drifted away from it. On an Interstate mind you!
5 hours to travel about 40 miles and I was totally beat when it finally turned to rain coming into Colfax. I thought I was flying at this point, but looking at my speedo it showed I was screaming along...at rip-snorting 35 mph.
They had closed the pass while I was coming over and the backup of eastbound I-80 cars turning around...must have been at least 20 miles long.