The Red Rock Geology: Born at the Edge of a Supercontinent
Near Sedona, Arizona
The red walls that surround you were built at the edge of the world. About two hundred seventy-eight million years ago, in the Permian period, this ground sat on the western margin of the supercontinent Pangaea, where a shallow arm of the sea met endless coastal dunes and tidal flats. Layer by layer, wind and water stacked sand here, and that sand is the rock you see today.
Geologists gave the most important of these layers a local name, the Schnebly Hill Formation, because it appears nowhere else on the Colorado Plateau in quite this way. It runs eight hundred to a thousand feet thick, and it is the source of almost every famous red cliff in Sedona. The color is iron.
Over millions of years, iron rich groundwater seeped grain by grain through the porous sandstone and left behind hematite, a form of iron oxide, the same compound as common rust. It coated each quartz grain and stained the stone from within, which is why the red runs all the way through and does not simply wash off. Cap this red sandstone with the pale cream Coconino Sandstone above, ancient wind blown dunes that never took the iron stain, and you get Sedona's signature contrast, a rusted castle wearing a white crown, visible for miles.
Look closely and you can read the sea itself. Inside the Schnebly Hill Formation sits a thin gray band called the Fort Apache Member, only ten to twelve feet thick, a layer of limestone left when a shallow sea briefly flooded the desert. Its surface still carries ripple marks pressed by tides that ran here nearly two hundred eighty million years ago.
All of this would still be buried if not for water. Oak Creek is young, less than six million years old, and where it cut down along an old fault, it stripped away the softer layers beneath the hard sandstone, so slabs broke free and the cliffs marched backward, opening a canyon up to two thousand feet deep. Every butte and spire you will pass today is what erosion left standing.
You are driving through a cross section of a vanished coastline.
