Weathering and erosion, the architects of the spectacular landforms found throughout the Colorado Plateau, could not have created the area's canyons, arches and domes if a few things hadn't happen first. 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 to support it, the rock buckled and cracked. The crevices, once far below the earth's surface, were brought to the top when a movement in the earths surface known as uplift caused the land to rise. Water, wind and ice broke the exposed rock into small pieces (mechanical weathering) and transported them to a new location (erosion).