The Entrada FormationThe Entrada formation was deposited in the middle Jurassic and is about 175 million years old. The Entrada formation is divided into three members. The bottom layer is known as the Dewey Bridge Member. This layer is directly below the Slickrock Member and consists of brick-red silty sandstone that forms crinkly beds. The middle layer is known as the Slickrock Member. This is the first layer that is visible in the picture (uppermost layer in picture) and is characterized by red cross-bedded sandstone that is responsible for forming cliffs and the world famous arches in Arches National Park. The uppermost layer of the Entrada is the Moab Tongue, which is made up of white cross-bedded sandstone (this is not present in this picture).