I lived in No. Calif. for years. You can take Hwy 49 through gold country and see the old gold mill in Coloma, and head up to Pilot's Hill and Georgetown. The Sacramento Zoo is wonderful and there is a great museum in Sacramento as well. San Francisco is a wonderful city to just drive around in--the hills, the cable cars, and the Golden Gate Bridge.
Highway 1 runs the length of California and is very scenic and twisty and you can see the giant redwood trees. And don't forget Yosemite National Park. So much to see--makes me homesick.