Why are Sedona's Red Rocks Red?

Sedona, AZ (Sedona.biz) - Answering that question will take 320 million years.  How much time do you have?  Okay, just a little geology joke to keep things light.  We'll try to speed up the timeline for you.

First, you should know that Sedona sits at the foot of the Mogollon Rim which is the southern most part of the Colorado Plateau and extends for 200 miles across central Arizona to the White Mountains and averages 7,000 feet high. 

The Mogollan Rim is just south of Flagstaff.  The height and location of the Colorado Plateau in Northern Arizona makes it a perfect spot for ponderosa pines. In fact, this region has the largest ponderosa pine forest on the continent.  The Colorado Plateau, of course, is where the Grand Canyon sits.

Brief History

About 320 million years ago, the area of Sedona lay under water in a sea, and the first layer of Sedona's rock formation came from the shells of sea creatures.  Later, rivers deposited sediment that is now red sandstone that easily erodes.  About 275 million years ago, sand that was eroded from ancient mountains and carried by ancient rivers was deposited in a delta, now Sedona.  In the Sedona area, sometimes a sea covered the land, and at other times the area of Sedona was a flood plain adjacent to the seacoast. Either way, sediment settled onto it. Rocks from this time constitute the most colorful rocks in the Sedona area and is commonly referred to as the Schnebly Hill Formation.  Eventually, about 1900 feet of rock covered the entire Sedona area.

The uplift of the Colorado Plateau several million years ago that created the Grand Canyon, also caused a cracking of the earth in the Sedona area. Earlier pressures caused by the movement of huge blocks of the earth’s crust also created cracks. Water followed the cracks and wore away the surrounding rock, resulting in creeks and streams. Because of this wearing away of rock during the last few million years in the Sedona area, we now have Bell Rock, Courthouse Rock, Cathedral Rock, and Coffee Pot Rock, as well as other cliff faces in the Sedona area. In general, they are capped by an erosion-resistant limestone that now protects the underlying softer layers from erosion.

So Why are the Red Rocks Red?

The answer is:  iron!  Sandstone is porous, and when water carrying dissolved iron drains through the sandstone, some of the iron is left behind, and it is this iron in the form of iron oxide, which is red, that coats the grains of quartz and gives it color.

The red rocks of Sedona, then, originated, some of them, from sediment in a sea or floodplain, while others originated from blown sand on dry land or in coastal areas. They can be distinguished by their colors, some more bright orange than others, some red, some tan. The bright orange rocks are more than 250 million years old. The white or grey rocks are either limestone that formed at the bottom of a sea, or else they are sandstone that has lost its red color because the color has been flushed out by water. There is also much basalt, extruded by volcanoes, in the area. 

Millions of years, sometimes hundreds of millions of years, went into the creation of what we now know as Sedona. A lot can happen in millions or hundreds of millions of years! Furthermore, the climate of Sedona changed over time - it has been under water, it has been a seacoast, and it has been a desert. Each type made its contribution to what is now Sedona. 

To see all of this mile by mile, follow the guided tour starting at Oak Creek Viewpoint (Oak Creek Canyon Vista) at the head of Oak Creek Canyon. The tour is found at the end of Sedona Through Time by Wayne Ranney (Flagstaff: Red Lake Books, 1993).