I drove solo to San Diego from Phoenix.
I made stops along the way at places that interested me
to stretch my legs and satisfy my curiosity.
11 miles from the Route 8 exit (one way) is the Petroglyph National Monument. It was $2.00 per car, and you paid via a cash envelope in a drop box. There is a camp host and picnic areas, covered and uncovered. There are no facilities. It is basically a desert wasteland of hot hotness.
My IPhone shut down from the heat (in October) because it was baking.
This site is a lower elevation, so you can camp here in January if you like sitting and staying in a place with no trees or water and lots of rocks. Like you are Wile E Coyote. I bet the sky is brilliant at night and I bet it is very quiet. There are 60 camp sites. They typically have room for drop ins, the camp host said. RVs are their most popular campers.
I parked and followed a very easy and obvious trail around the only thing to see a pile or rocks. Because I always do everything the wrong way, I started counterclockwise and that side of the rock pile does not seem to have petroglyphs so I was like yeaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaah.
Then because I had invested like zero energy, I bravely bore on the gravel circle path and was rewarded at about 12 noon on the clock with some petroglyphs and then an abundance.
It was surprisingly epic. There is sun banked signage explaining geology and native peoples and local water that used to be in this area. If you are easily entertained or need a reasonable and inexpensive stop to picnic between on Route 8. I recommend the National Monument.