I found this in the western part of the Santa Catalina Mountains in the mid-1970s. I like the fact that this otherwise strong object was vulnerable to steady pressure dissolution at points of contact. Instead of faulting or cracking the cobble, the directed tectonic stresses found a different way to ‘shorten’ the cobble.
Age & Formation
Quartzite pebble from the Barnes Conglomerate within the Apache Group, Mesoproterozic, ~1.1 Ga.