Arches National Park is a U.S. National Park in eastern Utah. It is known for preserving over 2000 natural sandstone arches, in addition to a variety of unique geological resources and formations. The park is located near Moab, Utah, and is 119 square miles (310 km2) in size. The national park lies atop an underground evaporite layer or salt bed, which is the main cause of the formation of the arches, spires, balanced rocks, sandstone fins, and eroded monoliths in the area. The arches of the area are developed mostly within the Entrada sandstone formation.