90% of the time you can get through with a 4wd. I believe there are conditions that CalTrans requires you to have 4wd/Awd and snow tires or chains. Then there is R5 which means you have to have AWD/4WD and chains. If they are letting you through with R5 conditions, it's not really worth it and the roads are going to close shortly anyway. Usually they close before that, but maybe 2-3 times a decade they'll let you through on that. True white knuckle driving no matter what you are in.