California is lucky to have the biggest, tallest and oldest trees. You could easily do a road trip where you see all three species. Here's my suggested itinerary.
Go in the fall. Spring is pretty in the mountains, but late snowstorms can throw a wrench in your plans and you can't do step 4 below until after the snow is cleared around late June or early July.
1. Fly to SFO or OAK and rent a car for a one-way trip.
2. Visit Muir Woods to see the coast redwoods (tallest). There are many other places to see Redwoods, but something about Muir Woods is special. Also, it's conveniently located if you're in the Bay Area. You do need to make a parking reservation for the day you're going to be there.
3. When you're finished exploring the Bay Area, head for the Giant Sequoias (biggest) in Yosemite National Park. There are more of them in Sequoia National Park than Yosemite, but the Mariposa Grove in Yosemite is also quite impressive and it's easier to get to from the Bay Area. Stay at the historic Wawona Hotel or if you haven't yet been to Yosemite Valley (or just want to see it again) try Yosemite Lodge. Yosemite hotels book up very early, so if you hope to do this trip this year, you need to start looking for cancellations ASAP. Book Yosemite lodging first and then plan the rest of the trip around whatever hotel room you find in that area. If you're completely unable to find anything in the park, then Fish Camp or El Portal have places to stay.
4. Afterwards, you can take Tioga Pass over the mountains and head for the Ancient Bristlecone Pine Forest (oldest).
5. Continue down the eastern Sierra and fly home from LA (BUR is easier than LAX) or Las Vegas. If you have time en route, stop at Mono Lake, Devils Postpile National Monument, Manzanar Historic Site, Death Valley National Park.
All these places can be enjoyed without any serious hiking, though you might walk a mile or at most two in some spots, and you definitely do not need to camp. If you do this trip, it's worthwhile to get a National Parks pass if you don't already have one.