Day 5 : Stop 3

DAY 5 (9/30/2025) - STOP 3

"White Sands National Park"

COORDINATES: 32.81764° N, 106.26198° W

Fig. 39 Jumping on a Dune in White Sands Landscape

    Our final stop of this trip brought us to White Sands National Park, which sits within the northern end of the Tularosa Basin. Geologically, the formation of this site began more than 250 million years ago, when the area was submerged beneath the shallow Permian Sea. During repeated cycles of evaporation, calcium and sulfate ions concentrated enough to precipitate thick deposits of gypsum on the seafloor, which later became part of the Yeso Formation now exposed in the surrounding San Andres and Sacramento Mountains (White Sands, NPS). These marine evaporites formed the essential source material that would become the gypsum sands seen presently.

Fig. 40 Lake Otero and Current Dune Field (NPS)

    Tectonic uplift during the Laramide Orogeny, roughly 70 million years ago, raised these Permian deposits and set the stage for later basin development (White Sands, NPS). The region was later stretched during the formation of the Rio Grande Rift around 30 million years ago, creating the Tularosa Basin and uplifting the adjacent fault-bounded ranges. These structural events produced a closed, internally drained basin which trapped sediments and dissolved minerals carried down from the mountains.

    Beginning in the late Pleistocene (24,000–12,000 years ago), cooler and wetter conditions transported runoff and glacial meltwater into an extensive lake system known as Lake Otero (fig. 40), which filled much of the Tularosa Basin. As water flowed down from Sierra Blanca and the mountain ranges, it dissolved gypsum from exposed Permian rock and the mineral-rich water into the lake (Geology of a Gypsum Dunefield, NPS). When the climate became more arid around 10,000 years ago, Lake Otero evaporated, leaving behind thick deposits of gypsum on the basin floor. The present-day Alkali Flat and Lake Lucero playas represent the last remnants of this ancient lake, and they continue to serve as active gypsum-producing sites during seasonal flooding and evaporation cycles (White Sands, NPS).

    Much of the sediment we observed at the site reflects this unique evaporite-dominated system. The primary “rock” is not lithified rock at all but gypsum sand grains derived from the breakdown of large selenite crystals that formed as Lake Otero dried. Because gypsum is extremely soft, the grains continue to abrade during transport, producing the white, powder-fine texture that characterizes the dunes. The texture of these sands is much different than that found in a beach landscape. 

    The active landscape at White Sands is dominated by these gypsum dunes (fig. 39), shaped by wind. Dune types vary depending on sand availability, vegetation, and wind intensity, and some migrate as much as several meters per year. Despite being in a desert, the dunefield is underlain by a shallow water table, which acts as a stabilizing layer that prevents the dunes from blowing away entirely and creates marsh-like interdunal flats after heavy rainfall (White Sands, NPS). This hydrologic influence contributes to the preservation and ongoing production of new gypsum sand. Wind, however, contributes to structures such as ripple marks in the sand (fig. 41). 

Fig. 41 Ripple Marks

External References:

Geology of a Gypsum Dunefield. (2025). Instructure.com; National Park Service U.S. Department of the Interior. https://usflearn.instructure.com/courses/1985970/files/folder/Field%20trip%20materials/White%20Sands?preview=199513348

White Sands. (2025). National Park Service Department of the Interior. https://usflearn.instructure.com/courses/1985970/files/folder/Field%20trip%20materials/White%20Sands?preview=199513314

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