A natural arch, natural bridge, or (less commonly) rock arch is a natural landform where an arch has formed with an opening underneath. Natural arches commonly form where inland cliffs, coastal cliffs, fins or stacks are subject to erosion from the sea, rivers, rain, snow melt and/or through a subaerial (under the air) weathering processes.

Most natural arches are formed from structures of sandstone or limestone at or near steep, often vertical cliff faces. Then after the passage of time spanning geological eras, the softer rock layers of the cliff face is eroded to a point which creates rock shelter or alcoves beneath the relatively harder caprock above the eroded areas. Too, when the harder caprock forms a narrow ridge formation through or across an area, the underlying softer rock will often erode from opposite sides of the formation causing the two sides of the eroding underlying softer rock area to eventually meet underneath the caprock layer, thus creating an arch or natural bridge.

The erosional processes exploit weaknesses in the softer rock layers making cracks larger and removing material more quickly than the caprock; however, the caprock itself continues to erode after an arch has formed, which will ultimately lead to collapse.

The choice of calling the formation either a natural arch or a natural bridge is somewhat arbitrary, however, both are cause by the erosive effects of water. A natural arch is said to be caused by the erosive water as it flowing down from above the formation, as in rain and/or snow melt. A natural bridge is said to be cause by the erosive water as it flow from under the formation, as in river flow and/or sea wave action.

48.523889, -64.199444

(34.0935243, -87.6151519)

(36.9079900, -110.0811724)

(34.89762775, -111.8076723)

(34.3228101, -111.4544827)

(35.6809600, -109.0493518)

6.9645241, -111.7798718

(34.0170001, -119.3568152)

Channel Island National Park

(38.4406500, -123.1262529)

4,606 feet (38.743517, -109.499341)

Height: 52 feet

4,607 feet (38.742759, -109.494008)

Span: 290 feet, Width: 18 feet, Height: 77.5 feet

(37.5317427, -112.2603544)

Elev. 5,693 feet (38.051933, -109.755124)

Height: 135 feet, Width: 120 feet

Elev. 5,653 feet (38.088321, -109.833181)

Height: 150 feet

Needles District of CNP

6,099 feet (38.38786, -109.863664)

pothole arch in Islands in the Sky District

5,819 feet (38.390261, -109.838176)

sandstone arch in Islands in the Sky District

(38.13982331366499, -109.77717107687059)

fractured sandstone arch

Cedar Meas formation in Needles District

Floor Elev. 4,309 feet (36.9191680, -111.4754518)

Colorado River watershed

(37.077222, -110.964167)

Length: 275 feet, Width: 33 feet, Height: 290 feet

Rainbow Bridge National Mounument

Access: Navajo Nation Lands, permit required

Floor Elev. 4,309 feet (38.607222, -109.531111)

Colorado River watershed

Elev. 4,315 feet (38.593593, -109.508728)

Length: 243 feet, Width: 18 feet, Height: 77.5 feet

Access: Grandstaff Trailhead (38.6098060, -109.5335402) 4-mile round trip

Elev. 6,427 feet (37.456653, -111.831567)

Height: 150 feet, Width: 92 feet

sandstone double arch

Elev. feet (38.605908926952885, -109.60226650059903)

Utah State Route 279

(38.579943, -109.619887)

Potash Road, Utah State Route 279

5,906 feet (37.423591, -113.157726`)

Length: 287.4, Width: 35 feet

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Natural Bridge Monument

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Natural Bridge Monument

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Natural Bridge Monument

(37.0775595, -110.964435)

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(43.4141, -89.7202)

Devil′s Lake State Park, Sauk County

(42.734134, -105.612216)

Bridge Creek and campground

10,777 feet (44.365556, -109.763889)

Shoshone National Forest (hike trail)

22.875147, -109.894171

12.541111, -69.958333

Collapsed on 2 September 2005.