Quiet Camping near Joshua Tree's Southern Entrance
The southern part of Joshua tree is the quieter end of the park (especially in the summer). We got up to watch the sunrise and didn't see another car for 2 HOURS.
The campground is sandy and dusty (as is the whole park since it's a desert), and each site has a concrete picnic table and a fire ring. Unlike most of Joshua Tree's campground, Cottonwood does have a water point (and flushing toilets)-- and it is just down the road from the Cottonwood Visitor Center (a very basic ranger station that also has bathrooms -- but no fancy gift shop of cafes like some other NPs)
Cottonwood is a great site if you are coming in from Palm Springs/Palm Desert/Coachella and you want to spend an incredible night under the stars. It's just 7 miles off of I-10, but there aren't any cities around so there isn't any distracting light in the sky. Also, because there aren't any cities around, bring whatever food and fuel you need. It's 40+ miles out of the park heading north to get gas, so make sure you get gas in Indio or Coachella when driving in.
Cottonwood is 20$ a night, (the other campgrounds without water are $15). During the summer sites are first come, and there were plenty to choose from -- There were only 3 other campers we saw there. Rumor is that this site is also last to fill up in the busy months because it is much further out of the way from the other campgrounds. Don't forget to fill up your water jugs before you leave if you're headed north deeper into the park.
If you want to make the Mastodon Peak hike (3 miles) or do the Lost Palms Oasis Trail (8 miles) this is best place to stay for an early morning start. I was lazy, and opted for a drive to the Cholla Cactus Garden, and a walk around the nature path.
There's not much privacy between sites since there aren't any trees -- and also no places to hang hammocks without some creativity.