We live in Southern California....Our favorite is to head up HWY 101 to Oregon. You'll see Solvang, Pismo, Hearst Castle, Carmel, San Francisco, redwoods, ocean, wine country on short side trips from the highway.
Even more adventurous is to travel up HWY 1 and then come back down HWY 101. Hwy 1 can have some weather issues fog, rain, wind and mudslides but the scenery is spectacular.
Another trip on our bucket list (we've done part of it) is to go up HWY 49 known as the Gold Country Highway. Here's some details https://en.wikipedia.org/wiki/California_State_Route_49
If you don't want to travel a lot then Anza Borrego or Joshua Tree Nat'l Monuments are great places to stay for days/weeks and hike or vegetate.