Mississippian Sea

(Photo by James Miller)

The most abundant rocks in Rock Canyon are limestones, formed mostly during the Mississippian Period.  These cliff-forming layers form most of the walls of the canyon.  They represent millions of years of deposition in a shallow marine environment.  All through the Mississippian Period (350-320 my)  Utah was covered by a warm shallow sea.  Limestone forms in conditions where the concentration levels of calcium carbonate (CaCO3) are such that they precipitate to form tiny crystals that drift to the bottom of the seafloor to form a layer of limy mud.  Small marine organisms also extract CaCO3 from the water the build their shells and hard parts.  When they die they also accumulate at the bottom to create a layer of limy material.  Through compaction and cementation, this limy material forms limestone.  These processes are highly sensitive to changes in climate, which are recorded in the multitude of very thin (centimeter-sized) layers in the carbonate rocks.