From LA to San Francisco there are stretches were 1 and 101 are the same road. All of the section where 1 is a separate it is very just fine. Generally two lane right on the coast and goes through towns. There are sections of 1 between San Francisco and Eureka that would would be an issue since they have 30' King Pin to Rear Axle restriction in places. This link Truck Network Map
will take you to a Calif DOT site that provides maps of the areas. You could probably drive through these areas but I would not recommend it. North of Eureka 101 follows the coast so there is no US 1. I have traveled 101 north all the way to Olympia WA. In fact we took 101 all the way to Port Townsend then the ferry over to Whiddbey Island. It was a very nice drive.