Looking at a satellite map of New Mexico, one is struck by two prominent features in the south-central part of the State. The first is a narrow, elongated swath of black, resembling spilled ink; this, in fact, is a basaltic lava flow. South of this flow is a blotch of white, representing extensive dunes of gypsum, the famous White Sands of New Mexico. Both of these geographic features are within the Tularosa Basin, which is flanked by the San Andres Mountains, to the west, and the Sacramento Mountains, to the east. The valley itself has an average elevation of 4000 feet.
During the Permian Period, some 250 million years ago, this portion of North America was invaded by shallow seas. Sedimentary rocks from these seas were uplifted as the Rocky Mountains formed, 70 million years ago. Then, about 30 million years ago, tectonic forces began to pull this region apart; the crust began to thin, upwellings of magma developed and the Permian Uplift was split in two. Today, the San Andres and Sacramento Mountains are remnants of that Uplift and are separated by the Tularosa Basin, the northernmost extension of the Chihuahuan Desert.
Throughout the wet climate of the Pleistocene, rain and snow eroded these mountains, sending mineral-laden waters into the enclosed Basin; with no outlet to the sea, Lake Lucero formed, covering the western half of the valley. As the climate began to dry, at the end of the Pleistocene, the Lake gradually retreated, leaving extensive, gypsum-covered playas in its wake. Southwesterly winds began to create the dunes of white, gypsum sand about 7000 years ago; the process continues today and the dune field now covers more than 275 square miles (half of which is protected within the White Sands National Monument).
Partly stabilized by drought tolerant plants such as dropseed, sandhill muhly, gyp gramma and soaptree yucca, the gypsum dunes are home to a fascinating variety of wildlife; some species, including the bleached earless lizard, Cowles prairie lizard and Apache pocket mouse, have evolved a white coloration, camouflaging them against the white sands. Other residents include kit fox, pallid bats, kangaroo rats, bobcats, western coachwhips, Sonoran gophers, western diamondback rattlesnakes and Texas horned lizards; orynx, an African antelope, have also been introduced to the area, threatening the fragile environment (they are fenced out of the National Monument).
Formation of the Tularosa Basin occurred in concert with regional volcanism; several Tertiary volcanoes dot the northern section of the Sacramento Mountains and are responsible for the formation of their higher summits (including Sierra Blanca). A smaller volcano, now represented by the Little Black cinder cone, west of Carrizozo, released the basaltic lava flow north of the White Sands; this flow occurred about 5000 years ago and lasted 30 years or more. Known as the Malpais (Badlands), the Carrizozo basalt flow is 40 miles long and up to 60 feet thick. The Valley of Fires Recreation Area, on the east side of the lava flow, is accessed by U.S. 380.
