An unnamed alcove natural arch, Mesa County, Colorado
Photo by Jay Wilbur
NABSQNO 12S-686515-4322867. For several years this natural arch was classified as an irregular natural arch. However, a close inspection in June 2009 revealed that there is a slit-like second opening east of the main opening shown above. This opening occurs along the same vertical joint that led to the formation of the main opening. This is convincing evidence that the arch is a very young alcove natural arch. The bluff it is in is Entrada sandstone. It is located east of 11 Road, about 6 miles northwest of Glade Park, Mesa County, Colorado. It has a span of about 45 feet.