siltstone

Sedimentary rock

Siltstone

Siltstone is a sedimentary rock which has a grain size in the silt range, finer than sandstone and coarser than claystones.

Description[link]

Siltstone is a clastic sedimentary rock. As its name implies, it is primarily composed (greater than 2/3) of silt sized particles, defined as grains 1/16 - 1/256 mm or 4 to 8 on the Krumbein phi (φ) scale. Siltstones differ significantly from sandstones due to their smaller pores and higher propensity for containing a significant clay fraction. Although often mistaken as a shale, siltstone lacks the fissility and laminations which are typical of shale. Siltstones may contain concretions. Unless the siltstone is fairly shaly, stratification is likely to be obscure and it tends to weather at oblique angles unrelated to bedding. Mudstone or shale are rocks that contain mud, which is material that has a range of silt and clay. Siltstone is differentiated by having a majority silt, not clay.

References[link]

• Folk, R.L., 1965, Petrology of sedimentary rocks PDF version. Austin: Hemphill’s Bookstore. 2nd ed. 1981, ISBN 0-914696-14-9
• Williams, Howel, Francis J. Turner and Charles M. Gilbert, 1954, Petrography, W. H. Freeman

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View of Monument Valley in Utah, looking south on U.S. Route 163 from 13 miles north of the Arizona/Utah State line

Monument Valley (Navajo: Tsé Biiʼ Ndzisgaii, meaning valley of the rocks) is a region of the Colorado Plateau characterized by a cluster of vast sandstone buttes, the largest reaching 1,000 ft (300 m) above the valley floor. It is located on the Arizona-Utah state line (around 36°59′N 110°6′W / 36.983°N 110.1°W / 36.983; -110.1), near the Four Corners area. The valley lies within the range of the Navajo Nation Reservation, and is accessible from U.S. Highway 163.

Geography and geology[link]

Location of Monument Valley in the United States.

The area is part of the Colorado Plateau. The floor is largely siltstone of the Cutler Formation, or sand derived from it, deposited by the meandering rivers that carved the valley. The valley's vivid red color comes from iron oxide exposed in the weathered siltstone. The darker, blue-gray rocks in the valley get their color from manganese oxide.

The buttes are clearly stratified, with three principal layers. The lowest layer is Organ Rock shale, the middle de Chelly sandstone and the top layer is Moenkopi shale capped by Shinarump siltstone. The valley includes large stone structures including the famed Eye of the Sun.

Between 1948 and 1967, the southern extent of the Monument Upwarp was mined for uranium, which occurs in scattered areas of the Shinarump siltstone; vanadium and copper are associated with uranium in some deposits (see Uranium mining in Arizona).

In media[link]

Monument Valley has been featured in many forms of media since the 1930s.

Tourism[link]

Monument Valley from the valley floor

Monument Valley is officially a large area that includes much of the area surrounding Monument Valley Navajo Tribal Park, a Navajo Nation equivalent to a national park. Oljato, for example, is also within the area designated as Monument Valley.

Visitors may pay an access fee and drive through the park on a 17-mile (27 km) dirt road (a 2-3 hour trip). Tours are also available, and the fee varies between about $40 and $100 per person depending on the services provided and route. Parts of Monument Valley are accessible only by guided tour, such as Mystery Valley and Hunts Mesa.

Horseback rides are also available from various establishments both inside the park and in the general Monument Valley area, and rates vary widely depending on the length of the ride. Rides may be only an hour, or overnight camping trips. Additionally, hot air balloon flights are available May 1 through October 31, and small airplane flights are sometimes available.

Monument Valley is part of the Grand Circle, which includes the Grand Canyon National Park, Mesa Verde National Park, Bryce Canyon National Park, Zion National Park, Capitol Reef National Park, Canyonlands National Park, Natural Bridges National Monument, Hovenweep National Monument, Arches National Park and many other attractions.

Gallery[link]

• 

  East Mitten and West Mitten Buttes

• 

  View from John Ford's Point

• 

  The North Window

• 

  The North Window

• 

  The Totem Pole

• 

  The Thumb

• 

  Three Sisters

• 

  Interior of a "male" style Navajo hogan, with a stove made from a 55 gallon drum

Monument Valley panoramics[link]

Monument Valley panorama, taken from the Visitor Center and showing the "Mittens" and the road which makes a loop-tour through the Park

Panorama of Monument Valley in Winter

Totem Pole

See also[link]

• Valley of the Gods

References[link]

External links[link]

Wikimedia Commons has media related to: Monument Valley

• Monument Valley Navajo Tribal Park website
• Map of Monument Valley
• Monument Valley Tours
• Los Angeles Times article about Monument Valley
• American Southwest Guide
• Energy Information Administration notes on uranium mining and its decommissioning
• IMDb list of movies and television shows with scenes in Monument Valley
• Column from PopMatters.com on Monument Valley in film

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