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Physiographic Provinces

A physiographic province is a region with a particular pattern of landforms that differs significantly from that of adjacent regions. Each province has a distinctive geologic framework and particular combinations of topographic and hydrographic features that have evolved through geologic time. The individual landforms (e.g., mountains, canyons, alluvial fans) that in aggregate make up the varied natural landscapes of a given province reflect a variety of geomorphic processes. In New Mexico these range from the action of deep‑seated (hypogene) forces, including volcanism and tectonism, to surficial (epigene) processes, such as erosion and sedimentation by water or wind.

 The Southern Rocky Mountain Province extends from Colorado into the north‑central part of the state as a twoprong system of high ranges separated by deep structural basins of the northern Rio Grande rift. The eastern prong of the Southern Rockies includes several ranges of the Sangre de Cristo Mountains between the San Luis and Espahola rift basins and the Raton Section of the Great Plains. The area east of Taos also includes the high, parklike Moreno Valley between the central Sangre de Cristos and the Cimarron Mountains. The western mountain prong between the Navajo Section of the Colorado Plateau and the Rio Grande rift basin includes the Brazos uplift to the north and the outlying San Pedro, Nacimiento, and Jemez mountains to the south. The latter highland areas, located south of the lower Chama Valley, are transitional to the southeastern Colorado Plateau and Basin and Range provinces.

The Sangre de Cristo, Brazos, and San Pedro‑Nacimiento ranges have cores of Precambrian crystalline rocks overlain by Paleozoic, Mesozoic, and lower Cenozoic sedimentary rocks. Cenozoic volcanic and sedimentary rocks cap the ranges in a number of areas. Numerous glaciated peaks and alpine valleys are present in the Sangre de Cristos north of Santa Fe and in the Brazos uplift near the Colorado border. Among these peaks is Wheeler Peak (13,161 ft), the high point of the state, northeast of Taos. Valleys draining areas of alpine glaciation (e.g., Chama, Costilla, Red, Embudo‑Santa Barbara, Nambe, Santa Fe, Pecos, Mora) have stepped sequences of glacial‑outwash terraces.

The Jemez Mountains west of Los Alamos (maximum elevation 11,561 ft) are primarily a constructional feature built by late Cenozoic volcanism. Eruptions of Pleistocene age produced the huge Toledo‑Valles caldera complex as well as the Bandelier Tuff that caps the Pajarito Plateau at the western edge of the Espahola structural basin.

The Southern Rocky Mountain Province also includes the San Luis Valley, a Rio Grande rift basin that is transitional southward to the Espahola Valley in the Basin and Range Province. At the southern end of the basin, the Rio Grande has cut a deep gorge (canyon walls up to 1,000 ft high) in the thick accumulation of Pliocene basalt flows that forms the central Taos Plateau. The eastern part of the plateau includes a constructional plain built by alluvial fans at the base of the Sangre de Cristos.

The Colorado Plateau Province in northwestern New Mexico is part of a larger region (extending into Arizona, Utah, and Colorado) characterized by erosional landscapes carved on relatively undeformed sequences of sedimentary and volcanic rocks. The Zuni Mountains between Gallup and Grants are the only major mountain uplift. The summit of the Mount Taylor volcanic center (elevation 11,301 ft) is the highest point in the New Mexico part of the province. Major landforms include scarp‑bounded tablelands (plateaus, mesas, buttes, and benches), cuestas, hogbacks, and a variety of valley and canyon types. The province straddles the continental divide (6,675 to 9,916 ft elevation range) and contains headwaters of the Rio Chama and Rio Puerco (Rio Grande system) on the east, and the San Juan and Little Colorado rivers on the west.

The Navajo Section of the Colorado Plateau is dominated by two structural basins with thick sequences of gently dipping Mesozoic and lower Cenozoic sedimentary rocks, mainly shale, mudstone, and sandstone with extensive coal seams. The large San Juan Basin lies between the Southern Rockies, the Four Corners platform, and the ZuniDefiance uplift. The smaller Gallup‑Zuni basin is located south and west of the Zuni Mountains. The Chuska Mountains (maximum elevation 9,370 ft), along the New Mexico ‑ Arizona border, are a tableland with prominent bounding escarpments. Prominent volcanic necks, such as Shiprock, in the Four Corners area north of the Chuskas result from exhumation of feeder conduits at middle Cenozoic volcanic centers.

Aside from narrow hogback belts eroded on steeply dipping strata of monoclines flanking major structural upwarps, the Navajo Section is characterized by broad rolling plains carved on easily eroded rocks, and cuestas and tablelands capped by gently dipping resistant sandstone beds. Canyonlands and escarpments of moderate local relief occur mainly in the eastern part of the San Juan Basin. However, most stream valleys are broad with relatively short canyon reaches; areas of high cliffs and escarpments are of limited extent.

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. The lowest point is the San Juan River channel near the Four Corners at the boundary between the Navajo and Canyonlands sections of the Colorado Plateau (elevation about 4,700 ft).

The only major perennial streams in the Navajo Section are the San Juan River, the Animas and La Plata rivers (which join the San Juan near Farmington), and the upper Rio Chama. The floodplains of these rivers are flanked by stepped sequences of fluvial terraces of Pleistocene age.

In the eastern part of the San Juan Basin, badlands are locally well developed on steep slopes carved on shaly sequences of late Cretaceous and early Cenozoic age. Partly vegetated aeolian sand sheets, with low eastnortheast‑trending dune ridges, and small active dune fields form extensive caps on upland surfaces in the central part of the Navajo Section, particularly between the San Juan and Chaco Valleys.

The Acoma‑Zuni Section, the southeastern subdivision of the Colorado Plateau, is a newly defined physiographic unit that includes the northern part of the area previously designated the Datil Section. The unit is bounded on the east by the Albuquerque Basin, a Rio Grande rift basin in the northern part of the Basin and Range Province. The Datil‑Mogollon (transitional) Section lies to the south.

The Acoma‑Zuni Section is characterized by extensive upper Cenozoic volcanics that form a discontinuous cover on erosional and constructional landforms typical of the neighboring Navajo Section. The northeastern Acoma‑Zuni area is dominated by Mount Taylor, a composite stratovolcano of Pliocene age, and nearby basalt‑capped mesas. Cabezon Peak at the northeast edge of the section is a particularly prominent plug‑type volcanic neck. To the west, the elongate upwarp of the Zuni Mountains (maximum elevation 9,265 ft), with a core of Precambrian crystalline rocks, is flanked by hogback and cuesta belts that have dipslopes and scarps capped by Permian and Triassic limestone and sandstone.

Broad plains south and east of the Zuni uplift are covered with Quaternary basalt flows and dotted with numerous cinder and lava cones. The Malpais Lava Field south of Grants contains the McCarty's basalt flow, which is about 1,000 years old and is the youngest volcanic unit in the state.

The Acoma structural sag and adjacent Lucero Uplift in the southeast part of the section include prominent sandstonecapped mesas and buttes of the Acoma and Laguna reservations. Limestone‑ and sandstone‑capped cuestas and benches of the Sierra Lucero area overlook the lower Rio Puerco Valley in the western Albuquerque Basin. As in the northern part of the section, many tablelands are capped with Pliocene basalt flows.

Much of the Acoma‑Zuni Section is drained by the Rio San Jose, the major tributary to the Rio Puerco. Downstream from its headwaters in the Zuni Mountains and Malpais Lava Field the river has few perennial reaches. Most narrow, deeply entrenched valleys of the San Jose system are south and east of the Mount Taylor volcanic field; elsewhere major valleys of the San Jose system are commonly broad, but still well entrenched below upland areas. Pleistocene basalt flows cap river terraces in the lower San Jose Valley downstream from Laguna.

The Datil‑Mogollon Section is part of a physiographic subdivision that is transitional between the Basin and Range Province and the Colorado Plateau. It is also a newly defined unit that includes the southern part of the area previously designated the Datil Section. This region of volcanic highlands extends into east‑central Arizona and contains several large structural basins and block‑faulted ranges. It is bounded on the east by basins of the Rio Grande rift, which are part of the Mexican Highland Section of the Basin and Range Province.

The Datil‑Mogollon volcanic field is the dominant geologic feature in this section and lavas and tuffs are the main rock types. Major landscape units are erosional remnants of huge cauldron structures with volcano‑tectonic depressions and resurgent domes. There are also remnants of large stratovolcanoes, mainly composed of basaltic andesite. High tablelands are capped with tuffs, andesite, and basalt lavas, and volcanic‑derived conglomeratic sandstones and mudstones.

The Datil‑Mogollon Section also straddles the Continental Divide (6,650 to 10,000 ft elevation range). The area west of the divide is drained by perennial headwaters of the upper Gila system, including the San Francisco and Tularosa rivers. Canyon incision by these streams has resulted in the deeply dissected tableland topography of the upper Gila River basin.

Internally drained structural basins (bolsons) and valleys of major ephemeral streams (arroyos) draining to the Rio Grande are dominant features east of the Continental Divide. San Augustin Plains, the floor of the largest closed basin (minimum elevation 6,780 ft), was the site of pluvial Lake San Augustin. Maximum elevation of shoreline features is slightly higher than 7,000 ft. 

Physiographic Provinces It

The Basin and Range Province includes much of central and southwestern New Mexico, and it extends into adjacent areas of Arizona, Chihuahua, and Texas.

The Mexican Highland Section includes two large areas of basin‑and range structure and topography separated by the valley of the Rio Grande. The Rio Grande rift depression coincides with the northern and eastern parts of the section. The Continental Divide crosses the bolson area west of the Rio Grande and is arbitrarily placed along the highest local drainage divides in the complex of internally drained basins between the Rio Grande and the Gila valleys.

Block‑faulted mountains commonly have Precambrian cores overlain by Paleozoic sedimentary sequences. Sandia Peak (elevation 10,682 ft), the highest point in the section, is at the crest of tilted‑fault block of this type. Organ Needle (elevation 9,012 ft) is the highest peak in the southern Mexican Highlands. Basin deposits which locally exceed 5,000 ft in thickness have several distinct basin‑fill facies, including piedmont alluvium, fine‑grained lake and playa sediments, coarse‑grained river deposits, and aeolian (wind‑carried) materials. Basalt fields are also locally extensive on basin plains; the youngest is the Carrizozo flow in the northern Tularosa Basin.

A number of the basin‑floor depressions were occupied by perennial lakes during Pleistocene glacial‑pluvial intervals. The largest late Pleistocene lakes, each about 200 square miles in area, were Lake Animas west of Lordsburg and Lake Otero in the Tularosa Basin west of Alamagordo. Large dune fields, including the White (gypsum) Sands of Tularosa Basin, are downwind from the pluvial‑lake plains and younger playa depressions.

The Rio Grande flows through an alternative series of broad and narrow valley segments that coincide with major structural basins of the Rio Grande rift, each separated by bedrock uplifts. The valley for the most part is incised from 300 to 600 ft into upper basin fill and associated volcanics. The only major canyon reach is Whiterock Canyon, east of the Pajarito Plateau, where the river cuts through the thick basalt sequence of the Cerros del Rio volcanic field.

The Gila River crosses the northwestern Mexican Highlands (north of Lordsburg) in a valley setting very similar to that along the Rio Grande. The low point of the Mexican Highland Section (about 3,700 ft) is at the Arizona border near Virden.

The Sacramento Section is characterized by high tablelands with broad, rolling summit plains; cuesta‑form mountains, with eastward dipslopes and west‑facing escarpments; and widely separated structural basins. Highlands, such as the Sacramento and Guadalupe mountains and Chupadera and Glorieta mesas, are capped with gently dipping limestone and sandstone of Permian age. Gypsum is commonly interbedded with limestone and sandstone sequences, and summit plains of tablelands and cuestas include extensive areas of karst depressions where dissolution of calcium sulfate and carbonate has taken place. Large limestone cave systems, such as Carlsbad and Fort Stanton caverns, are present in the Guadalupe and Sacramento highlands.

The Sierra Blanca igneous‑intrusive and volcanic terrain is the highest part of the province. Sierra Blanca Peak (elevation 12,003) is the southernmost glaciated peak in the continental United States. Topographic relief between Sierra Blanca and the adjacent Tularosa Basin (twenty miles to the west) is about 7,600 ft, making this the area of greatest local relief in New Mexico. Other highlands formed by igneous‑intrusive masses are the Capitan, Carrizo, Jicarilla, and Gallinas mountains.

The Estancia Basin, in the northwest part of the section (minimum elevation 6,050 ft), is a shallow structural basin, extensively modified by dissolution of gypsum, and by water and wind erosion. Basin fill is less than 500 ft thick and contains lacustrine and aeolian deposits. Lake‑shoreline elevations range up to about 6,350 ft. Holocene deflation has excavated numerous playa depressions, including Laguna del Perro in the basin floor. Small Pleistocene‑lake basins and Holocene playas near Pinos Wells and Encino are located along an ancient spillway route from the Estancia Basin toward the ancestral Pecos Valley.

The Great Plains Province occupies the eastern third of New Mexico and includes parts of three sections.

The Pecos Valley Section includes the terraced valleys of the Pecos and Canadian rivers and flanking piedmont plains and tablelands. Inner river valleys range from reaches with broad floors, occupied by floodplains and low terraces, to relatively shallow canyons. Elevation of the Pecos Valley floor ranges from about 5,300 ft near Anton Chico at the section's northwest corner to 2,840 ft at Red Bluff Reservoir on the Texas border. The latter site is the lowest point in New Mexico.

Higher piedmont erosion surfaces west of the Pecos are cut on eastward ‑di ppi ng Permian rocks and are transitional to surfaces in the Sacramento Section, highlands. Broad upland plains and tableland summits have caliche caprocks developed on veneers of upper Tertiary piedmont deposits.

The Pecos Valley Section extends southward and eastward into western Texas along the lower Pecos, Portales, and lower Canadian valleys. The Portales Valley east of Fort Sumner is a segment of the ancient upper PecosBrazos river valley that was abandoned by middle Pleistocene time. The High Plains borders are commonly marked by escarpments cut in sedimentary sequences with caliche caprocks. These features include Mescalero "Ridge" east of Roswell and "The Caprock" escarpment south of Tucumcari. The bold Canadian Escarpment forms the boundary with the Raton Section to the north.

Much of the Pecos Valley Section is underlain by Permian bedrock units composed of gypsiferous and saline evaporites, limestone and dolomite, mudstone and shale, and sandstone. Dissolution of evaporite and carbonate units is an active geomorphic process affecting landscape evolution in much of the region, and solution‑subsidence depressions at a wide range of scales are common landforms. Several solutionsubsidence basins southeast of Roswell have areas of many square miles, A stepped sequence of valley‑border surfaces also flanks the inner valleys and canyons of the Pecos and Canadian rivers. These surfaces are inset below the high‑level piedmont plains and reflect alternating intervals of valley incision and relative base‑level stability during Pleistocene glacial‑interglacial cycles. Quaternary wind‑formed deposits mantle large areas of older valley‑border surfaces east of the Pecos and north of the lower Canadian rivers.

Thick alluvial fills of late Tertiary and Quaternary age are present in broader central valley areas along the Pecos south of Santa Rosa, in the Canadian Valley northeast of Tucumcari, and in the Portales Valley

The Llano Estacado Section in New Mexico occurs as three separate areas that are western extensions of two major piedmont plateaus in the Panhandle region of Texas and Oklahoma. The plateau south of the Canadian Valley and the Caprock escarpment are designated the Llano Estacado or Staked Plains. In east‑central New Mexico this area is bisected by the Portales Valley The Staked Plains north of the Canadian Valley are also called the Panhandle subsection and are transitional westward to basalt‑capped piedmont plains of the Raton Section. The Llano Estacado is characterized by a nearly flat to undulating surface with a slight southeastward gradient. Elevations range from about 5,000 ft at the northwest edge to 3,500 ft near Hobbs.

Alluvial and aeolian deposits of the Ogallala Formation, with a resistant caliche caprock, underlie much of the High Plains surface. The caprock zone of secondary carbonate accumulation is at or near the surface along plateau edges and in most of the Llano area south of the Portales Valley. Elsewhere the Ogallala is usually buried by sandy to clayey deposits. Surface drainage throughout the area is poorly developed; shallow valleys of ephemeral streams cross the High Plains only at wide intervals. The broad uplands between stream valleys are dotted with thousands of small, shallow depressions, many of which contain playas and have low arcuate dune ridges on their eastern (downward) margins. The dominant process involved in basin formation appears to be deflation. However, water erosion of basin sideslopes and dissolution of soluble constituents of underlying deposits may also play an important role in depression formation and enlargement.

The Raton Section is characterized by high piedmont plains, of both erosional and constructional origin. Extensive basalt flows protect many of the highlevel surfaces from erosion. Deep canyons of the Canadian and Cimarron river systems are cut below these pied mo nt‑su rface remnants in the southcentral and northeastern parts of the section. To the south, stripped structural plains are abruptly terminated by the Canadian Escarpment, which borders the Pecos Valley Section.

Some of the most striking features of the Raton Section are the numerous late Cenozoic volcanic centers, such as the andesitic Sierra Grande stratovolcano (8,720 ft) southeast of Raton, and the extensive plains and tablelands capped by basalt flows. High mesas near Raton, such as Johnson and Bartlett mesas, are capped by basalts that were emplaced during the period of High Plains surface development. Extensive younger basalts west of Clayton and Wagon Mound cap remnants of the High Plains surface and associated piedmont alluvial deposits. Basalt flows of Pleistocene age, such as the Maxon Crater, and older Capulin flows cap river terraces within the Mora, Canadian, and Dry Cimarron canyons. The youngest Capulin flow locally covers the floor of Dry Cimarron Canyon north of Folsom.

Sedimentary rocks, for the most part broadly folded and gently dipping, underlie much of the Raton Section. Erosion surfaces on these units include the highly dissected Park Plateau west of Raton and the Trinidad escarpment which overlooks broad central plains near Springer. Extensive surfaces, such as Rayado and Charette mesas, are capped by upper Tertiary basalts.

Much of the southeastern third of the Raton Section is characterized by broad tablelands capped by an extensive sandstone unit (Dakota‑Mesa Rica). Tableland summits include the broad rolling plains of the Las Vegas Plateau west of the Canadian Canyon and more dissected mesa areas to the northeast between Ute Creek and Dry Cimarron valleys. A large High Plains outlier extending north from Mosquero is located between the Canadian Canyon and Ute Creek Valley. This constructional surface is mantled with piedmont alluvial deposits and has a caliche caprock.