It does look like river rock in those bottom photos.
It does look like river gravel. I really liked the orbital photo of the aluvial fan coming out of the creek. However, it appears that there are several meteor impact craters in the area that are more recent than the hydrological activity. That tells me that the flowing water ceased many millions, if not over a billion, years ago.
yes, the stuff on the lower left looks like typical Earth gravel