Boundaries

Part of the Rio Grande complex, this ecoregion covers most of the Mexican state of Chihuahua and extends into southwestern New Mexico. A small portion of the ecoregion is found in northeastern Sonora and extreme southeastern Arizona. The southwestern extent of this ecoregion is defined by the mountains of the Sierra Madre Occidental. Additionally, a small portion of the ecoregion lies on the western side of the Continental Divide within Arizona.

Topography

Topography ranges from the hills and plains of the Chihuahuan desert to the rugged Sierra Madre Occidental, where peaks may exceed 3000 m.

Freshwater habitats

Freshwater habitats in this ecoregion include creeks, rivers, and springs. Most basins in this complex include headwaters, middle reaches, and terminal lagoons. Part of this ecoregion is the region known as Médanos Samalayuca, a harsh area of parched sand dunes that was once the bed of an ancient lake.

Description of endemic fishes

As is typical of many endorheic habitats, the Guzmán - Samalayuca ecoregion is rich in endemic species. Species that are strictly endemic to the ecoregion include the largemouth shiner (Cyprinella bocagrande), carbonera pupfish (Cyprinodon fontinalis), and Chihuahua chub (Gila nigrescens). Near-endemics include the Cahita sucker (Catostomus cahita), Bavispe sucker (C. leopoldi), whitefin pupfish (Cyprinodon albivelis), and Palomas pupfish (C. pisteri).

Justification for delineation

Ecoregion delineations were based on qualitative similarity/dissimilarity assessments of major basins, using the standard administrative hydrographical regions of the Mexican federal government. High endemicity of several taxa, as indicated in the species list, evolved through the isolation of springs and interior basins that comprise the ecoregion.

Level of taxonomic exploration

Deficient. There are few roads near headwaters.