Recently found a structure in Egypt that is like a kiva and they don't know what it's use was either. Appears much of the southwest rock structure is water carved but early geologist think it was mostly wind erosion. Some alluvial and volcanic too but that is mostly around rivers. IIRC Grand Canyon has 2 or 3 volcanic 'dams' that are mostly gone now. Also a theory that canyons were from a release of the water from the plains states lake. Natural dam broke and G.C. & others formed. End of glaciers (10k yrs ago) formed the lakes and started the civilization is S.W., so they say.