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Navajo National Monument is located in the western section of the Navajo Reservation in northeastern Arizona (figures 1a and 1b). The monument consists of three noncontiguous sections: the Betatakin Unit (160 acres), the Keet Seel Unit (160 acres), and Inscription House Unit (40 acres). The elevation of the Betatakin Visitor Center is 7,400 feet (2,220 m). The Keet Seel section is located about 8 miles (13 km) northeast of Betatakin and contains one of the most important large Pueblo ruins in the Southwest. The Inscription House section is located 40 miles (64 km) west of Betatakin in Nitsin Canyon.
Navajo National Monument is part of the Colorado Plateau Physiographic Province, an uplifted area that encompasses portions of Colorado, Utah, Arizona, and New Mexico. Uplift and subsequent erosion have carved deeply incised canyons into relatively horizontal layers of sandstone and exposed colorful, flat- lying sedimentary rock formations in this part of the Colorado Plateau. Navajo National Monument is located north of U.S. Highway 160 on the Shonto Plateau, a subregion of the Colorado Plateau (figure 2). The Organ Rock Monocline, an uplift that underlies U.S. Highway 160, separates the largely Jurassic and Triassic rocks exposed at the surface of the Shonto Plateau from the Cretaceous rocks of Black Mesa. Black Mesa encompasses 5,400 square miles (14,000 sq km) of flat plains, mesa, and incised drainages south of U.S. Highway 160 (Kamilli and Richard 1998; Blakemore and Truini 2000).
Tsegi Canyon is the primary drainage of the eastern part of the Shonto Plateau. It contains three major branches and countless side branches cut deeply into the Navajo sandstone. Betatakin and Keet Seel are located in two of the arteries of the canyon. Side canyons contain numerous other prehistoric ruins (NPS 2001).
Tsegi Canyon has eroded into Triassic- Jurassic strata (figure 3). The primary formations are part of the Jurassic Glen Canyon Group. The formations in the Glen Canyon Group are, from youngest to oldest: the pale salmoncolored, cross- bedded Navajo Sandstone that formed from an ancient sand dune field; the purplish siltstones and cross- bedded sandstones of the Kayenta Formation which record the remnants of a large river delta or floodplain; and the cross- bedded Wingate Sandstone, another preserved sand dune field (Cooley et al. 1969; Chronic 1983; Peterson 1994).
Springs and seeps are associated with the contact between the cliff- forming Navajo Sandstone and the underlying Kayenta Formation. The Navajo Sandstone is porous and permeable and serves as a regional aquifer, while the Kayenta is the confining bed. At the contact, groundwater moves laterally, emerging as springs along the canyon walls.
Three layers of alluvial deposits are present in Tsegi Canyon and comprise the following formations: the Jeddito Formation (late Pleistocene), the Tsegi Formation (early Quaternary about 2000 B.C. to A.D. 1), and the Naha Formation (A.D. 1450- 1880) (Schafer et al. 1974; Karlstrom 1982). A buried paleosol marks the erosional boundary between the Jeddito and Tsegi. The younger Tsegi - Naha boundary is marked by terrace relationships (Karlstrom 1982). The type localities for the Tsegi and Naha Formations are in Tsegi Canyon, which is one of the few places in the southwest where the beginning of arroyo cutting is well documented. Tsegi Canyon is now part of the Tsegi Canyon Navajo Tribal Park (NPS 2003). These formations are represented on the GRE digital geologic map as Quaternary alluvium (map symbol: Qal).
The Colorado Plateau is a relatively rigid lithospheric block that, while uplifted, has not experienced the severe deformation present in the surrounding Rocky Mountain or Basin- and- Range physiographic provinces. While extensive thrust faults deformed the Rocky Mountains during the Laramide Orogeny (Late Cretaceous � Middle Tertiary) and rifts in the earth�s crust pulled apart the Basin- and- Range (Miocene Epoch), the Colorado Plateau was bent and folded into broadly warped anticlines and regionally extensive monoclines. The entrance drive to the monument climbs the Organ Rock Monocline that rises from the east to west onto barren outcrops of the Navajo Sandstone. Once on the crest of the monocline, the strata dip only two to three degrees to the southwest (Cooley et al. 1969).
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