Look, while the suggestions to narrow your focus are not bad ones...
(What would you say to someone coming to see "all of the UK in 10 days"
California *is* as big as your lovely island )
I'd actually not mess around with the bookings you already have. Why stress yourself out with second-guessing? You can have a *lovely* 10 day vacation flying into LAX & flying out of SFO. Rather than trying to hit everything California has to offer, why not focus on the classic coastal route North to San Francisco.
Day 1: Fly into LAX & stay overnight
Day 2: Leisurely drive to Santa Barbara
(possible diversions: beaches, outlet malls, orchid farms, and strolling around Santa Barbara itself, which is an eminently lovely downtown to stoll from the pier to the Presideo, even the Mission if particularly ambitious)
Day 3: Explore the Santa Barbara Wine Country & stay somewhere about Pismo Beach
(possible diversions: wine tasting, Solvang Danish colony, Santa Maria BBQ, more beaches)
Day 4: Cambria
(possible diversions: beaches, fun & funky towns San Louis Obisbo & Morro Bay, historic missions)
Day 5: Drive Highway 1 to Monterey
(possible diversions: MUST BOOK TOUR of Hearst Castle!!!, scenic views, Carmel)
Day 6: Drive to SFO
(possible diversions: LOTS OPTIONS depending on route & time! Monterey Aquarium? I'd certainly drive up to the fun & funky town of Santa Cruz for lunch on the boardwalk, do you want to see redwoods? Driving highway 9 to Felton gets you to amazing groves and a steam railway, on the other hand, if you are not burned out on amazing coastal scenery, continuing on Highway 1 and coming in San Francisco from the "back way" through Pacifica is pretty amazing)
++++++++++++++++++++++++++++++++++++++++++++++++++ ++
Yes, you will miss Yosemite, Sequoia, and the Sierras, which is a pity. You won't have a chance to hit Napa and the Northern wine regions (although they are much pricey than the Southern ones). You'll miss the North Coast redwoods which are a touch more amazing than the ones south of SFO. You miss Lassen, which has been described as California's Mt. Fuji. And we haven't even mentioned San Diego, Palm Springs, the Colorado River, or anything of the amazing experiences in my own home town of Los Angeles.
I guess you'll just have to hit it big like Rowling...
And come back!
