It kinda looks like a parking lot for visitors. Camels, atv's and the such. Could also be that their having a monster truck demonstration and the
mounds are a course. My guess is the photo was taken just before the concession stands were in place.
The only way to know is really to check it out. If there were some people there it's definitely possible [certain] to obtain precious artifacts or
find glyphs to help us figure out by whom, when, why the pyramids were built.