Navajo section

The Navajo Section is a physiographic section of the larger Colorado Plateaus province, which in turn is part of the larger Intermontane Plateaus physiographic division.^[1] It is located in northeastern Arizona and northwestern New Mexico, is named for the Navajo Nation reservation, with about half of the area of the section in the reservation, and are characterized by broad rolling plains carved on easily eroded rocks, and cuestas and tablelands capped by gently dipping resistant sandstone beds. The lowest point in the section is about 4,700 ft., near the Four Corners area, where the boundary between the Navajo Section and the Canyon Lands section is, is in the San Juan River channel. The highest point in the New Mexico part of the Navajo Section is at Chromo Mountain (elevation 9,916 ft) on the Continental Divide near Chama.^[2] One of the most prominent features of the Navajo Section is the Ship Rock, near the town of Shiprock.

Geology and physiography

The area is predominately generally horizontal sandstone beds with some shale sequences of late Cretaceous and early Cenozoic age. A few areas of the section also have abundant volcanic necks and buttes, but due to the arid weather and soft sandstone, many of the rock formations of the area have eroded to form distinctive features of long cuestas, shallow canyons and valleys, narrow fan terraces, undulating plateaus, isolated mesas, steep hills, and some shale badlands.^[2]

Near the Four Corners area is a steeply tilted monocline known as The Hogback, which trends southwestward from where the San Juan River enters the area. Here the San Juan River flows into an area known as the San Juan Basin, where the western San Juan Basin is typified by exposures of the Fruitland and Menefee Formations. A stepped sequence of high stream terraces, present above the San Juan River and its tributaries, represents abandoned Pleistocene flood plains.^[3]

References

1. ^ "Physiographic divisions of the conterminous U. S.". U.S. Geological Survey. http://water.usgs.gov/GIS/metadata/usgswrd/XML/physio.xml. Retrieved 2007-12-06. 
2. ^ ^{a b} Hawley, John W.. "New Mexico’s Environment, Physiographic Provinces". http://www.nmmastergardeners.org/Pdf%20FILES/NM's%20Environment.pdf. Retrieved 2007-12-25. 
3. ^ Soil Survey of Shiprock Area, Arizona and Apache County, Parts of San Juan County, New Mexico. National Cooperative Soil Survey. pp. 14. http://soildatamart.nrcs.usda.gov/Manuscripts/NM717/0/Shiprock.pdf.