Anza Borrego Desert SP allows dispersed camping in certain areas of the park, and this is one of them.  I tried to find it on the website, but found no mention of allowed camping in the park.  However, it's listed in the visitor guide you can get from the visitor center.

The reviews on The Dyrt for the camping area directly across the street to the north of this section mentioned that there will be a campground built and fees charged in the near future, but I don’t think that’s the case for this side of the street. There was no signage or any signs of development here on this corner. Just lots of boondockers tucked in among all the shrubs, plenty of room for everyone. 

I could see this area getting annoying with ATVers on the weekends, but there were none when we were there mid week in April. A couple of obvious sketchy long termers there, with heaps of junk and posted signage to stay away, which wasn’t a problem as there was plenty of space to stay far away from them. 

Good cell service and beautiful sunrise. 

Watch for nails and broken glass.:(