Before the introduction of domesticated livestock in the late 19th century, virgin grassland carpeted Otero Mesa. It was far from homogeneous, however: differences in soil composition, climate, and surface runoff created a patchwork of unique plant communities, or ecological sites. Specifically,

"[a]n ecological site is defined as a distinctive kind of land with specific soil and physical characteristics that differ from other kinds of land in its ability to produce a distinctive kind and amount of vegetation and its ability to respond similarly to management actions and natural disturbances."^[28]

Scrublands on Otero Mesa are not considered unique ecological sites. Instead, they are classified as degraded states of other ecological sites whose historic climax plant communities (HCPCs) were grassland. Black grama, blue grama, tobosa, alkali sacaton, vine mesquite, bush muhly, and dropseeds were the dominant species in these HCPCs; the dominant species in non-riparian, degraded flatland ecological sites are now creosote bush and honey mesquite.

The only major throughway on Otero Mesa is U.S. Route 180, which crosses the plateau to between El Paso and Guadalupe Mountains National Park.^[1] There are no towns on Otero Mesa.^[1] The western edge of Otero Mesa in New Mexico is defined by an abrupt escarpment.^[1] McGregor Range, a U.S. Army installation, extends from U.S. Route 54 over this escarpment and onto Otero Mesa proper.^[1] While access is restricted on McGregor Range, the public can use the Owen Prather Highway (New Mexico State Road 506) to cross it. This is the only way onto Otero Mesa from the west in New Mexico. NM-506 experiences temporarily closures during some military exercises.

Otero Mesa slopes gently eastward into Crow Flats and Salt Flats. These two playas drain most of the plateau. The western edge of Otero Mesa is an escarpment continuous with the Sacramento Mountains. In the vicinity of El Paso, Hueco Mountains separate Otero Mesa from the Rio Grande Valley. Until Van Horn, the border of Otero Mesa is a series of steep escarpments and bajadas. At its southwest corner, Otero Mesa dramatically rises to form the Sierra Diablo, which tower over Salt Flats. Otero Mesa fades into the lowlands for 40 miles before it reaches the tablelands of the southern Sacramento Mountains.

Otero Mesa is the southern extension of the eastward-dipping Sacramento Mountains fault block. The extension of the Rio Grande rift has gradually uplifted the fault block over the last 25 million years. Several exposed sedimentary formations compose the bedrock of the Mesa. From west to east, these are the Hueco Formation, Yeso Group, and San Andres Formation.^[56] This is also the relative chronology of the formations, from oldest to youngest. All are Permian marine carbonate sequences deposited during the Cisuralian epoch.

Sacramento Mountains Bajada edit

In contrast to their abrupt western escarpment, the southern margin of the Sacramento Mountains is a gently sloping bajada. The bajada is formed by three alluvial fans emerging from the mouths of Wildcat Canyon, El Paso Canyon, and the Sacramento River Canyon. The superficial alluvium of the bajada was deposited between 126,000 kya and the present day.

Along with the outflow of Piñon Creek onto Crow Flats, the Sacramento Mountains Bajada is the primary groundwater recharge zone in the Salt Basin.

Cornudas Mountains edit

The Cornudas Mountains are field of igneous intrusions on the New Mexico-Texas state line. Rising dramatically from the plains of Otero Mesa, these plutons "represent the northern extent of the Trans-Pecos magmatic province."

The igneous intrusions that compose the Cornudas Mountains were emplaced between 37.4 mya to 31.6 mya. This corresponds to the end of the Laramide Orogeny and the "progressive shallowing of the subduction of the Farallon plate beneath the North American plate." In the succeeding time, the plutons were exhumed by erosion, being more resistant to weathering than the surrounding sedimentary rock.

Lithology edit

In the Cornudas Mountains, "the predominant lithology is porphyritic nepheline syenite," though other alkalic rocks, including "nepheline-bearing augite syenite,...nepheline-bearing trachyte,...syenite,...nepheline syenite,...phonolite,... foliated porphyritic nepheline syenite,...quartz-bearing syenite,...quartz-bearing trachyte" and nepheline-bearing augite syenite are present.

Mining edit

"The Cornudas Mountains have been examined for potential economic deposits of gold, silver, beryllium, rare-earth elements, niobium,...uranium, [and nepheline,] but no production has occurred."

Minerals edit

Windmountainite edit

Wind Mountain is the type locality of windmountainite, a novel mineral there discovered in a phonolite dike. Windmountainite was formally described in 2020.

Georgechaoite edit

Wind Mountain is the type locality of georgechaoite, where it occurs in miarolitic cavities in nepheline syenite. Georgechaoite was formally described in 1985.

Brokeoff Mountains edit

The Brokeoff Mountains are a series of southeast-dipping fault blocks that form a disjunct the Guadalupe Mountains. Three major formations are exposed in the Brokeoff Mountains: the Yeso, San Andres, and Grayburg formations (listed from oldest to youngest). All are composed of Cisuralian marine deposits.

The rugged terrain of the Brokeoffs and southern Guadalupe Mountains escarpment form a distinct, northward-opening "V." Big Dog, Upper Dog, and Middle Dog Canyons lead to the apex of the V, the uplands of Guadalupe Mountains National Park.

Otero Mesa is a 1.2 million acre (4,900 km²) area in northern Chihuahuan Desert region of southern New Mexico. Between 1954 and 1965 the U.S. Army expanded its McGregor Range facilities at Fort Bliss onto Otero Mesa by purchasing ranches.^[57][58] In 2005, the Bureau of Land Management approved the area for exploratory drilling for oil and gas,^[59] but that approval is currently being litigated^{[citation needed]} by the state of New Mexico and environmental groups who want the mesa to be recognized as protected wilderness.

On Tuesday, April 28, 2009, the Court of Appeals for the Tenth Circuit ruled against the US Bureau of Land Management plan for leasing the Otero Mesa for oil and gas extraction. The court found that the BLM had failed to consider an alternative that would leave the Otero Mesa unleased, and also failed to examine potential impacts to the underlying groundwater. The oil company HEYCO had been granted a lease for extracting natural gas form Otero Mesa, pending the outcome of the litigation.^{[citation needed]}