The Sedona area was at sea bottom 330 million years ago, and the shells of sea creatures formed a layer of limestone that underlies the area today, called the Redwall limestone because of its color, the result of iron oxide deposited in the rocks by water in later eras. The Supai Group of red sandstone, deposited when the area was a floodplain about 300 million years ago, sits atop the Redwall Formation, to a depth of about 600 feet. On top of that is a layer called the Hermit Formation, about 280 million years old, made of sandstone, mudstone and conglomerate.
The Middle Period
On top of the Hermit Formation is a layer that 270 million years ago was coastal sand dunes, and is now red sandstone up to 700 feet thick in places. Two more layers of sandstone were then capped by a layer of limestone laid down when the sea returned about 255 million years ago and is known as the Kaibab Formation.
The Final Phase
The so-called Laramide orogony--a round of mountain building that created the Rocky Mountains between 80 million and 35 million years ago--lifted the Sedona area and caused cracks that provided channels for water flowing from the new mountains. Water erosion widened the cracks into broad valleys, leaving only islands of the original layers above the Hermit Formation, in the form of the red buttes, spires and towers that now surround Sedona as silent sentinels from a remote past.