Weathered and eroded, these isolated rock formations make up Monument Valley in southeastern Utah and northern Arizona. Formed by sandstone deposits and geologic uplift, the valley’s buttes and mesas sit around 5,600 feet above sea level and spans roughly 91,700 acres. (Image ID# desert)
erosion, desert, cliffs, desert varnish
Erosional remnant, Mitten Rock, Monument Valley, Arizona, USA. (ID# WE-12)
Buttress Unconformity, northern Arizona. In buttress unconformities, the younger material
is deposited against the older material, resulting in the apparent truncation of the younger rock. On
closer inspection, however, one can see erosional features along the contact to indicate its depositional
origin. (ID SrU-25)
If you look at Time 1, you can see a coastline in cross-section, with sand being deposited closest to shore, mud a little farther out, and eventually carbonate material even farther out. As sea levels rise in Time 2, the sites of deposition for these materials migrates landward, putting mud deposition on top the earlier sand deposition and so on. In time 3, the sequence moves even farther landward, resulting in carbonate over mud over sand. If these materials become preserved and turned into rock, they form the sequence sandstone overlain by shale overlain by limestone – just what we see on top the Great Unconformity. (Image ID# transgression)
