naturalarches.org: A natural arch is a rock exposure that has a hole completely through it formed by the natural, selective removal of rock, leaving a relatively intact frame.

Hippiepunkpirate's elaboration: The Colorado Plateau features the most famous arches in the world, and are usually made of sandstone. Arches National Park in Utah obviously the mecca of this phenomenon. These features are also fairly common throughout the desert southwest, and can be found in other rock types.

A big controversy is how to define the difference between a natural arch and a natural bridge. The Natural Arch and Bridge Society (NABS) (naturalarches.com) defines a natural bridge as a type of natural arch. Using the NABS definition and criteria, a separate label has been created for natural bridges. According to NABS, a natural bridge meets at least one of the following:

- a current of water, such as a stream, clearly was a major agent in the formation of the opening (hole)
- a current of water, such as a stream, flows through the opening (hole)
- it is being, or has been, used by man as a bridge supporting a portion of a road
- it has the general appearance of a man-made bridge, e.g., a flat, level top over an arched opening

If the arch you are labeling meets one of the above criterion, please label it under "natural bridge". If it does not meet one of the above criterion, please label it under this page (natural arch). Windows, such as Window Rock rock near Canyon de Chelly, are natural arches.

Examples:
Delicate Arch in Arches National Park, Utah would be labeled "natural arch".
Sipapu Bridge in Natural Bridges National Monument, Utah would be label "natural bridge".