I stayed at Arroyo Salado one year during a super bloom at Anza Borrego Desert State Park.  The campground is very, very basic.  You pull up and find a spot and camp.  There are no designated campsites.  And it's free.  There are pit toilets, which are clean and don't really smell.

We had the pleasure, as I said, of coming during the super bloom, when all of the sites closer to town were booked.  This is in the "badlands" part of the park, leaving Borrego Springs and heading toward Salton City, which happens to be the cheapest place to get gas in these parts.

There's room to pitch a tent.  You basically set up camp wherever there is room. We were among blooming desert lilies and had to be careful not to damage any, but plenty of fairly flat sandy soil to pitch a tent.  You can bring your own barbecue if you want a fire, but fires must be self contained and you have to pack out what you bring in, so don't leave behind your ashes or coals.  Want to be lazy?  Grab dinner from one of the restaurants in town.

This part of the park (the badlands) tends to be slightly warmer than other areas of the park.  (Because of elevation and topography? I'm not sure why.)  This is a dry camp.  There is no water, so you have to bring your own. But Borrego Springs is maybe 15-20 minutes away if you need a supply run.

During the blooms and when it's not super hot, it's lovely, but it's ungodly hot in the summer here (110-115 degrees), not cooling much at night.  There are off-road roads in this area.  We watched a lovely moonrise amid some night-blooming flowers.  So time it right and it's lovely.