Plains of San Agustin

[1] Geologically, the Plains of San Agustin lie within the Mogollon-Datil volcanic field, just south of the southeast edge of the Colorado Plateau, and west of the Rio Grande Rift Valley.

There is no evidence of tectonic activity in the area after Lake San Agustin became extinct.

[4] Ecologically, the plains lie near the northern end of the Chihuahuan Desert (though the ranges surrounding the Gila River headwaters intervene), which is dominated by shrublands.

The plains were chosen for the observatory because of their isolated location away from large population centers, and the partial shielding effect of the surrounding mountain ranges.

The edges of the plains have sites of archaeological interest such as a prehistoric rockshelter known as Bat Cave.