One very cool aspect of a vertical contact (and unconformity) like this is that it is pretty obvious that the older unit (in this case the cross bedded sandstone) must have been fully lithified before the younger unit was deposited. In this case the was a slot canyon in the DeChelly that was filled in in the Late Triassic. Actually Triassic topography is visible here. You can stand on the end and look inot where the canyon would have been about 220 million years ago.
13 hours ago in Variety of Life