Erosion, the architect of the spectacular landforms found throughout the Colorado Plateau, could not have created the area's canyons, arches and domes if it weren't for some really old salt. Believe it or not, what is today a high desert was once an inland sea. When the seas retreated 300 million years ago, they left behind a really thick layer of salt. Over time, deposits, mainly sand, covered the salt and were compressed into a hard crust scientists call sedimentary rock. Salt, being the weaker of the two, eventually yielded to the pressure of the rock and was squeezed up and out like toothpaste from a tube. With nothing under it to hold it up the rock cracked and eventually collapsed. When movement in the earths surface known as uplift caused the land to rise, the crevices left by the salt were exposed making it easy for water, ice and wind to move the rock causing erosion.