California is a country disguised as a state. San Francisco, Los Angeles, and San Diego are three completely different cities; between them lie Big Sur's cliffs, wine country, the Sierra Nevada, Yosemite, Lake Tahoe, and deserts that look like another planet. No single trip covers it all — the state is 800 miles long.
The classic first trip is the coast: San Francisco, down Highway 1 through Monterey and Big Sur, to Los Angeles and San Diego. The second trip adds Yosemite and wine country. The third adds Tahoe, the desert parks, and the far north.
California's seasons vary by region: the coast is mild year-round (with summer fog in San Francisco), the mountains are snowbound in winter, and the deserts are only pleasant October–April. September and October are the secret best months almost everywhere.
California suits road trippers, food and wine lovers, families (Disneyland, San Diego), hikers, and skiers. Distances demand a car outside the big cities.