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. 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 Schnebly Hill Formation is a dark red sandstone, 800 to 1000 feet thick, that is the major component of the “Red Rocks” of Sedona. Unlike the Coconino, the Schnebly Hill sandstone is layed down in flat-bedded horizontal layers, interspersed with multiple thin white layers of limestone conglomerate. Both the flat strata and the limestone are indicators that the layer formed under water.