Pleistocene vertebrates from southeastern New Mexico
— Gary S. Morgan and Spencer G. Lucas

Southeastern New Mexico (SENM) has a wealth of Pleistocene vertebrate faunas. There are 40 named sites, with three major concentrations: 11 open sites in the Sacramento Mountains in Lincoln and Otero counties; 12 open sites in the Pecos River Valley and its tributaries in Chaves and Eddy counties; and 11 cave sites in the Guadalupe Mountains in Eddy County. Most open sites are dominated by large grazing mammals, including Mammuthus, Equus, Bison, and Camelops. Important open sites are Jal in Lea County with 13 species of vertebrates, Roswell from gravel pits near the Pecos River in Chaves County with 8 species, and Dry Gulch in the Sacramento Mountains in Lincoln County with a partial skeleton of Mammuthus columbi. Notable faunal records include Paramylodon harlani from Jal and Roswell, Smilodon gracilis from 25 Mile Stream in Eddy County, Panthera atrox from Jal, and Mammut americanum from Jal and Piñon in Otero County. Pendejo Cave in Otero County and the Guadalupe Mountains caves in Eddy County, including Burnet Cave, Dark Canyon Cave, Dry Cave, and Muskox Cave, among others, sample 98% (253 of 259 species) of the vertebrate species known from Pleistocene sites in SENM and 70% (253 of 367 species) of the species known from Pleistocene sites in New Mexico. Although most of these are extant species, 20 extinct megafaunal mammals are known from caves in SENM, including 8 species unknown from open sites in this region: Nothrotheriops shastensis, Canis dirus, Arctodus simus, Miracinonyx trumani, Tapirus sp., Navahoceros fricki, Euceratherium collinum, and Oreamnos harringtoni. Pleistocene cave faunas from SENM contain many extant species of small mammals no longer found in this region, including 5 species of Sorex, Marmota flaviventris, Thomomys talpoides, Neotoma cinerea, Lemmiscus curtatus, 4 species of Microtus, and Sylvilagus nuttallii. Most of these small mammals are now found at higher elevations in the mountains of northern New Mexico, indicating cooler temperatures and more available moisture in SENM during the late Pleistocene.