I found this spotted wall in the Navajo sandstone when I was investigating the Roman Bath at Pink Pocket (see album). Anyone have a theory how this formed? All I can think of is that they are stains from concretions that fell out of the wall, but I haven’t seen anything else quite like it on a vertical surface. I did see some spots on a horizontal surface of sandstone at Valley of Fire once. Notice that the spots appear on both sides of the bedding plane that cuts through the center of the picture, and through the crossbeds.
Update: I found more places like this in May 2018. Some of the dots had concretions embedded that had not fallen out yet. That must be what’s happening here.
