Text modified from Abell et al. 2000. Freshwater Ecoregions of North America: A Conservation Assessment. Island Press, Washington, DC, USA. Additional text provided by Jennifer Hales.


United States

Major Habitat Type

Xeric freshwaters and endorheic (closed) basins

Drainages flowing into

The Pecos joins the lower Rio Grande to flow into the Gulf of Mexico (Smith & Miller 1986). 

Main rivers to other water bodies

The major river in this ecoregion is the Pecos, and its drainage area defines the extent of the ecoregion. Major tributaries to the Pecos, virtually all of which arise in the mountains, include the North Seven River, Rio Penasco, Rio Felix, Rio Hondo and its tributary Rio Bonito, Ciénega del macho, and Alamosa Creek. Five major reservoirs have been constructed on the Pecos: Los Esteros Reservoir, Lake Sumner, Lake McMillan, and Avalon Reservoir in New Mexico, and Red Bluff Lake in Texas. Amistad Reservoir, built on the Rio Grande, inundates 10 to 20 km of the Pecos River at its confluence with the Rio Grande (Williams et al. 1985).



This ecoregion, part of the Rio Grande complex, extends from east-central and southeastern New Mexico into western Texas.


The topography of the Pecos ecoregion varies greatly, ranging from 3700 m in the Sangre de Cristo Mountains in north-central Mexico to 366 m at the confluence with the Rio Grande in southwestern Texas (Williams et al. 1985; Minckley et al. 1986). Late Tertiary alluvium blankets the eastern side of the New Mexican Mountains and High Plains on either side of the Pecos River valley (Smith & Miller 1986).

Freshwater habitats

The river contains a variety of habitats, including high-gradient, rocky-bottomed areas; sluggish, soft-bottomed meanders; and rocky riffles.

Terrestrial habitats

Most of the southern and central part of the ecoregion is dominated by the dry grasslands of the Chihuahuan Desert, with species such as bush muhly Muhlenbergia porteri), blue grama (Bouteloua gracilis), and big sacaton (Sporobolus wrightii) (McClaran 1995). Along the eastern edge these grasslands transition to the Western Short Grasslands ecoregion, dominated by grama and buffalo grass (Buchloe dactyloides). At higher elevations in the north and west, the grasslands are replaced by Colorado Plateau shrublands, Arizona Mountains forests, and Colorado Rockies forests (Ricketts et al. 1999).

Description of endemic fishes

There are no strict endemic species in this ecoregion.

Justification for delineation

Ecoregion boundaries are taken from Abell et al. (2000) and are based on subregions defined by Maxwell et al. (1995).


  • Abell, R. A.,Olson, D. M.,Dinerstein, E.,Hurley, P. T.,Diggs, J. T.,Eichbaum, W.,Walters, S.,Wettengel, W.,Allnutt, T.,Loucks, C. J.;Hedao, P. (2000). "Freshwater Ecoregions of North America: A Conservation Assessment" Washington, DC, USA: Island Press.
  • Minckley, W. L., D. A. Hendrickson, and C. E. Bond (1986). "Geography of western North America fishes: description and relationships to intracontinental tectonism" C. H. a. E. O. W. Hocutt (Ed.) The zoogeography of North American freshwater fishes New York: John Wiley & Sons.
  • Page, L. M., and B. M. Burr (1991). "A field guide to freshwater fishes: North America north of Mexico" New York, NY: Houghton Mifflin Co..
  • Ricketts, T. H.,E. Dinerstein,D.M Olson;C.J. Loucks (1999). "Terrestrial ecoregions of North America: A conservation assessment" Washington, D.C.: World Wildlife Fund.
  • Smith, M. L. and Miller, R. R. (1986). "The evolution of the Rio Grand Basin as inferred from its fish fauna" C. H. Hocutt and E. O. Wiley (Ed.) The zoogeography of North American freshwater fishes ( pp. 457-485 ) New York, New York, USA: Wiley.
  • Williams, J. E., Bowman, D. B., Brooks, J. E., et al. (1985). "Endangered aquatic ecosystems in North American deserts with a list of vanishing fishes of the region" Journal of the Arizona-Nevada Academy of Sciences 20 pp. 1-62.
  • Köppen, W. (1936). "Das geographische System der Klimate" Köppen W. and R. Geiger (Ed.) Handbuch der. Klimatologie ( (Vol. 1, pp. 1–44 ) Berlin, Germany: Gebrüder Borntröger.
  • McClaran, M. P. and Devender, T. R. V. (1995). "The desert grasslands" Tuscon, AZ: University of Arizona Press.