My suggestion would be to take a more northerly route as the western deserts, especially southwest deserts, will be scorching in June and in July there can be torential monsoon downpours. Not so good for camping.

Moab is amazing, but you will have to plan your physical activities to avoid the middle time of the day, as it will be very hot then.

If you start from Denver, you could also head for RMNP and do a bit of hiking loop through trail ridge and head for Moab, spend a day there, then head west via Bryce and Zion and on to LA. Bryce and RMNP are at higher elevation, so hopefully not so warm.

Is there a reason you want to go all the way to California? You might see more by spending less time on the road and more time in the parks. If Moab is high on your places to visit, consider flying into Grand Junction.

Need I remind you of the dangers of slot canyons that time of year?

I don't mean to be negative but there are particular difficulties, especially that time of year, so just be aware. Watch '127 Hours' before you go.

What do you most want to see in California? With the limited amount of time, I would stick with Colorado and Utah and possibly Wyoming.
Fly to Denver and spend the night. Take the Amtrak California Zephyr (morning departure) to Grand Junction. Rent your car there and make a big loop from there covering Moab, (Arches Canyonlands) and then head for Goblin Valley, Rt. 12, Bryce and Zion. Return the car to Grand Junction and if you still have an extra day make a stop at Glenwood Springs. The scenery from the train in the Glenwood Canyon is amazing if you are not driving through it on I-70.
California is another trip flying to San Francisco.

Thanks everyone! What are slot canyons?

The purpose of California was simply because I have never been. I have been to 15 countries but still haven't seen the majority of the U.S. I realize going to just one big city in CA isn't the same as seeing the state but I thought the 15 hour drive would make a good road trip and then could fly out of CA. I'm a quick traveler, usually spending 2 nights in each location. However, maybe just CO and Utah would be enough for a 1-1.5 week trip.

"What are slot canyons?"

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