Eventually enough soft material is weatherd away that it undercuts the cap layer, which subsequently breaks off in large slabs and falls into the canyons. Water running off the edge of the escarpment eats away at the lower layers, creating the shear cliffs. The steepness of the terrain is due the fact that the top layers of the strata are composed of basalt and limestone, which are harder than the underlying sandstone. The deep red color for which Sedona is famous is due to the presence of hematite (iron oxide, otherwise known as rust) that stains the sandstone of the Schnebly Hill and Hermit Shale layers. In the Sedona region, erosion has gradually eaten away at the rim, moving it northward a distance of about four miles and leaving behind some of the most spectacular and picturesque canyons and buttes found anywhere in the world.

The Mogollon Rim is about 200 miles long, and ranges between 20 feet in height.

Sedona is located just at the base of the Mogollon Rim, an escarpment that runs east-west through the middle of Arizona and defines the boundary between the Colorado Plateau to the north, and the Basin and Range to the south.

Arizona flat worm fossils