The entire region spanning Arizona and Colorado used to be a vast desert with sand dunes during the Jurassic period. Over time, the sand dunes began to form layers consisting of sand, silt, and gravel and harden. These deposits eventually became the Navajo sandstone, which is a sedimentary rock, that forms the walls of the canyons we see today. The rich coloring and different hues of red and orange that one sees on the walls are caused by the oxidization of iron in the rocks with time. The next stage of the Antelope Canyon formation began with the uplift of the Colorado Plateau, leading to flash floods, erosion, and ultimately the formation of the slot canyon.