An unnamed buttress natural arch in Mesa County, Colorado
Photo by Craig Shelley
NABSQNO 12S-676800-4326475. This unnamed buttress natural arch is eroded through Entrada sandstone. It is located above Knowles Canyon in a BLM wilderness area west of Grand Junction in Mesa County, Colorado. Access requires a permit and directions from the BLM ranger station in Grand Junction. The arch has been referred to as "Pentagon Arch" because of the appearance of its opening when viewed from an airplane, but this name is rather inappropriate and confusing. It has a span of about 15 feet.