Looks like a bunch of BMX style frames, if not actual BMX's. I would definitely say a dumping ground for a thief or somebody that really sucks at riding...
It's probably the homeless guy living a few bushes down on the right
I noticed when that bum set up camp by there and now there's a bunch of trash and stolen bikes laying around in that area
Next time I go by there I'll take pics of his camp, trash, and stolen bikes then stop by the Police Dept on my way home and see if they want the pics, If the cops got a map of that dry lake bed wooded area, I'll show them where his camp is too