IMG_2954

?? Looks sort of like a layer of hardened sediment.

Pretty much what it is. This is tufa, a freshwater limestone deposited from agitated water out of water that is pretty much saturated with calcium carbonate. It's essentially the same as travertine. This is a shoreline tufa from Pleistocene Lake Lahontan--the surf zone furnished the agitation. Tufas like this are extremely common out in that area.