We have returned from a trip to Joshua Tree National Park We were with Wilderness Volunteers. We stayed at the Black Rock Campground.
The campground has water and flush toilets. There is a dump station with a 5$ fee. No showers at the campground.
It is a good campground and quiet during the week. (Unless you have 60 MBA students from USC staying there with 45 cases of beer, it seems they need help understanding camping)
The campground sits in a small valley protected on 3 sides by small hills. We had a wonderful lighting and rain show one night. Fairly good star gazing although there is some bleed over from LA lights. I learned to better appreciate the desert with this trip and the work we did with Wilderness Volunteers.
I would recommend this as a destination.