California leads the nation in National Parks with nine, more than even Alaska which has 8 NPs. They are all pretty spectacular. Here are my favorites in order: Yosemite, Channel Islands (if you scuba dive), Joshua Tree, Death Valley, Sequoia, Kings Canyon, Redwoods, Mt Lassen and Pinnacles. Besides those you have the entire Pacific Coast Highway from San Diego to Crescent City. Along the way is the San Diego Zoo, Morro Rock, Big Sur, Monterey Aquarium, and the Point Reyes National Seashore. Lake Tahoe should have been a National Park as it is more beautiful than most of them.