Turns out, it's like Sleeping Beauty's castle surrounded by thorns. The mound is the high point of the ruin -perhaps the remnants of a platform? There is apparently a small ruin atop the mountain peak at the distance –Sunset Mountain, which may link visually to the Agua Fria plateau via an intermediate fort.

There are also the remnants of an aquaduct somewhere among those burrs. It's visible from Google Earth but I wasn't up for wading through all this to find it.