Rising high above the floor of Lexington Canyon, this imposing natural arch was created by the forces of weather working slowly over a span of centuries. Lexington Arch is unusual in one important respect: it is carved from limestone. Most of the natural arches of the western United States are composed of sandstone. The fact that Lexington Arch is made of limestone leads to speculation that it was once a passage in a cave system. Flowstone, a smooth glossy deposit that forms in caves has been found at the base of the opening, lending support to this theory.