I live in the desert and am familar with retention basins. But I was looking for any type of man-made structure (a berm or concrete weir for example), but haven’t found any yet.
There is a berm there I believe. If you go back to the picture posted here of the area, it would be at the bottom right of the warning area, about elev. 5000ft I’d guess.
I haven’t been up in those hills so I don’t know. Cottonwood Springs is a bit further up in the hills.