The Rocks

The Mississippian limestones, which make up the major part of the canyon walls, were deposited in a shallow warm sea that covered this area for tens of millions of years. The layered sedimentary rocks are mostly thinly bedded limestones that accumulated in a basin that was subsiding (the floor of the basin was sinking) due to the extension of the crust. Some layers of shale and sandstone can be found in the cliffs (yellow vs grey layers). The clastic sedimentary rocks represent fluctuations in sea level across vast expanses of the continent. (Photo by James Miller)

Limestone is composed of calcium carbonate (CaCO3).  It will effervesce when in contact with a dilute 10% solution of hydrochloric acid.  This is one method of identifying limestone in the field. (photo by Bill Harris)