Day Four: Tracing the Rift – Bottomless Lakes, the Rio Grande, and White Sands

 

Reference map for day four stops. Basemap sources: National Geographic Society and i-cubed (2013); Esri, TomTom, Garmin, FAO, NOAA, USGS, OpenStreetMap contributors, and the GIS User Community. Additional data: PermianBasin_Boundary_Structural_Tectonic. Map created by Brittney A. Hawley in ArcGIS Pro 

Stop 1: Bottomless Lakes State Park

Our last day of the journey begins with Bottomless Lakes State Park. The park sits on the eastern edge of the Pecos River Valley, about 14 miles southeast of Roswell, and includes most of a chain of nine lakes formed through karst processes in the Seven Rivers Formation of the Artesia Group. The lakes were named for their bottomless appearance and for the local cowboys who, according to legend, tied their ropes together yet still couldn’t find the bottom  (Mclemore, 1999; NMBGMR, 2025).

Spring-fed lake at Bottomless Lakes State Park, formed by karst processes in the Pecos River Valley

Each lake occupies a collapse sinkhole created when groundwater dissolved underlying gypsum and limestone, causing the overlying rock to cave in. Where these depressions intersect the water table, spring-fed basins formed, their deep blue and turquoise hues reflecting both depth and mineral content . The surrounding cliffs expose alternating layers of dolomite, gypsum, and red siltstone, showing that these lakes developed within ancient back-reef and sabkha deposits tied to the Permian reef complex farther south (McLemore, 1999).

Even today, the system remains dynamic: groundwater continues to circulate through the subsurface, while high evaporation rates concentrate minerals within the lakes. Bottomless Lakes offers a vivid example of how ancient depositional environments and modern hydrologic processes intersect to create New Mexico’s distinctive karst landscapes.

Stop two: Rio Grande Rift 

On our way toward White Sands, we made a brief stop overlooking part of the Rio Grande Rift, a major continental feature that stretches from southern Colorado through New Mexico into northern Mexico. The rift marks an area where the Earth’s crust is being pulled apart, forming a series of fault-bounded basins separated by uplifted mountain blocks. Extension began around 30 million years ago and continues at a slow rate today, shaping the valleys that now host the Rio Grande River. (USGS, 2023)

From our stop, the broad, flat valley floor and distant fault-scarred uplands offered a clear view of this active tectonic landscape. Although we only paused long enough for photos, the rift provides an important link between the region’s tectonic evolution and surface processes, influencing drainage patterns, groundwater flow, and even the location of volcanic activity throughout central New Mexico. 

View across the Rio Grande Rift toward the Tularosa Basin. The white flats visible at the base of the mountains are the Alkali Flat of White Sands

        Last Stop: White Sands National Park 

The story of White Sands National Park also begins with the Permian Sea. As sea levels rose and fell over millions of years, enormous gypsum deposits accumulated on the seafloor. Around 70 million years ago, tectonic forces associated with the Laramide orogeny uplifted these ancient marine rocks, exposing what would become the Tularosa Basin.

Fast forward to about 30 million years ago, as the Rio Grande Rift began to pull the continental crust apart, magma upwelled and the region stretched, creating a series of fault-bounded basins and uplifts. One of these basins was the Tularosa Basin.

During the Pleistocene Epoch, the climate here was far wetter, and a large lake known as Lake Otero filled much of the basin. Gypsum from the surrounding Permian formations was dissolved by rainwater and carried into the lake by surface runoff and groundwater. When the climate warmed and the lake eventually dried, thick beds of gypsum were left behind on the basin floor. (National Park Service, 2020-a)

Over time, these deposits were mechanically weathered, breaking down into fine gypsum sand grains that could be carried easily by wind. This is the process that gave rise to the vast, brilliant dunes that now ripple across White Sands National Park, an otherworldly landscape born from ancient seas, tectonic stretching, and the relentless power of wind.

Picture of the vastness of the dunes at White Sands National Park taken at sunset

Geologically, the dunes are in constant motion. Prevailing southwesterly winds push the gypsum grains into crescent-shaped dunes, while occasional wind reversals create cross-bedding. This is where thin layers intersect at opposing angles, and are visible in many of the dune faces. Smaller ripple marks develop on the windward slopes, while steep avalanche faces form on the leeward sides as sand cascades downward. (National Park Service, 2020-a)

Bedding planes within the gypsum dunes show intersecting layers that record changes in wind direction and dune migration over time

Between the dunes are interdune flats, areas where the water table lies just beneath the surface. Here, thin gypsum crusts form as moisture evaporates, leaving behind hardened layers that preserve subtle sedimentary features. These crusts, ripples, and cross-bedded layers record the ever-changing direction and strength of the winds shaping the dunes, providing a living example of aeolian processes in action. (NMBGMR, 2020)

Wind ripples across the gypsum surface at White Sands National Park

Wind ripple and alignment patterns on the surface of the gypsum sands at White Sands National Park. These shallow ridges form as wind direction and speed fluctuate, organizing sand grains into parallel linear features across the dune flat

The last recommendation I have is to mix a little fun with your geology! At White Sands, you can rent sleds or bring your own, and spend some time gliding down the dunes. Sledding down the steep, powdery gypsum hills was not only exciting but also a great way to appreciate the scale and beauty of this remarkable landscape. 

   End of the Trail – Reflections from the Field

Our journey through southern New Mexico revealed more than just striking landscapes, it uncovered a story written in stone, sand, and time. From the deep-marine limestones of the Bone Spring Formation to the towering Capitan Reef, the quiet springs and caves, and finally the luminous dunes of White Sands, each stop told a chapter in Earth’s long narrative of oceans rising and falling, continents stretching, and minerals transforming. Along the way, we stood inside ancient reefs, traced evaporite layers born in vanished seas, and even sledded down dunes made from gypsum that once settled on the Permian seafloor. What makes this region so extraordinary is the continuity of its record, how every formation connects across millions of years of geologic change. It’s a humbling reminder that the landscapes we explore today are living remnants of deep time, shaped by processes that continue to sculpt our planet.

Photo of our field trip group taken by our professor, Bogdan P. Onac

Resources: 

Anderson, R.Y., Dean, W.E. (1995). Filling the Delaware Basin: Hydrologic and Climatic Controls on the Upper Permian Castile Formation Varved Evaporite. In: Scholle, P.A., Peryt, T.M., Ulmer-Scholle, D.S. (eds) The Permian of Northern Pangea. Springer, Berlin, Heidelberg. https://doi.org/10.1007/978-3-642-78590-0_4

Bebout, Don G., and Charles Kerans, editors. Guide to the Permian Reef Trail, McKittrick Canyon, Guadalupe Mountains, Texas. New Mexico Bureau of Mines and Mineral Resources, 1989.

Burger, P. A. (2007). Walking guide to the geology of Carlsbad Cavern. Carlsbad Cavern & Guadalupe Mountains Association.

 Dean, Walter E.; Kirkland, Douglas W.; and Denison, Rodger E., "Parent Brine of the Castile Evaporites (Upper Permian), Texas and New Mexico" (2000). USGS Staff -- Published Research. 307. https://digitalcommons.unl.edu/usgsstaffpub/307

EarthDate. (2023, May 9). Carlsbad Caverns (Episode 315). Bureau of Economic Geology, University of Texas at Austin. Retrieved from https://www.earthdate.org/episodes/carlsbad-caverns 

King, P. B. (1948). Geology of the Guadalupe Mountains, Texas. U.S. Department of the Interior, National Park Service. https://www.nps.gov/parkhistory/online_books/gumo/215/index.htm

McLemore, V. T. (1999). Bottomless Lakes State Park. New Mexico Geology, 21(2), 51–55. https://geoinfo.nmt.edu/publications/periodicals/nmg/21/n2/nmg_v21_n2_p51.pdf

Melim, L. A., Northup, D. E., Spilde, M. N., Jones, B., Boston, P. J., & Bixby, R. J. (2001). Evidence for microbial involvement in pool finger precipitation, Hidden Cave, New Mexico. Geomicrobiology Journal, 18(3), 311–329. https://doi.org/10.1080/01490450152467813

National Park Service. (2020). Overview of the geology of White Sands National Monument. U.S. Department of the Interior, White Sands National Monument. Retrieved from https://www.nps.gov/whsa/learn/geology-of-white-sands.htm

National Park Service. (2022, November). Salt Basin Dunes – Guadalupe Mountains National Park. U.S. National Park Service. https://www.nps.gov/gumo/planyourvisit/dunes.htm

National Park Service. (2025, May 6). Cave / Karst Systems. U.S. Department of the Interior. Retrieved October 25, 2025, from https://www.nps.gov/cave/learn/nature/cave.htm

New Mexico Bureau of Geology and Mineral Resources (NMBGMR). (2020-a). Geology of White Sands. In P. A. Scholle, D. Ulmer-Scholle, S. M. Cather, & S. A. Kelley (Eds.), The Geology of Southern New Mexico’s Parks, Monuments, and Public Lands (Sample Chapter).  Retrieved from https://geoinfo.nmt.edu/publications/guides/nmparks/southern/WSandsSampleCh.pdf

New Mexico Bureau of Geology & Mineral Resources. (2020-b). “Sitting Bull Falls Recreation Area,” in The Geology of Southern New Mexico’s Parks, Monuments and Public Lands. (Peter A. Scholle, ed.). Retrieved from https://geoinfo.nmt.edu/tour/home.cfml?id=76

New Mexico Bureau of Geology and Mineral Resources (NMBGMR). (2025,  April 9). Geologic Tour: Bottomless Lakes State Park. Retrieved from https://geoinfo.nmt.edu/tour/state/bottomless_lakes/home.html

Recreation.gov. (n.d.). Parks Ranch Cave, Carlsbad Field Office Recreational Caves: Near Carlsbad, New Mexico. U.S. Department of the Interior. Retrieved November 5, 2025, from https://www.recreation.gov/camping/poi/10276158

Scholle, P. (2000). Geologic road log: El Paso, Texas to Carlsbad, New Mexico. New Mexico Bureau of Geology & Mineral Resources. Retrieved October 19, 2025, from https://geoinfo.nmt.edu/tour/federal/parks/PermianReef/fieldtrips/ep_csbd_roadlog.html#stop1-1a

Scholle, P.A., R.H. Goldstein, and D.S. UlmerScholle. 2004. Classic upper Paleozoic reefs and bioherms of west Texas and New Mexico. Socorro: New Mexico Institute of Mining and Technology.

Stafford, K. W. (2013). Evaporite karst and hydrogeology of the Castile Formation: Culberson County, Texas and Eddy County, New Mexico. In L. Land, D. H. Doctor, & J. B. Stephenson (Eds.), Sinkholes and the Engineering and Environmental Impacts of Karst: Proceedings of the Thirteenth Multidisciplinary Conference (NCKRI Symposium 2, pp. 123–131). Carlsbad, NM: National Cave and Karst Research Institute. https://doi.org/10.5038/9780979542275.1120 

Swanson, B. (1986). Rattlesnake Springs Historic District (National Register of Historic Places Registration Form). National Park Service. Retrieved October 25, 2025, from https://npshistory.com/publications/cave/nr-rattlesnake-springs-hd.pdf

U.S. Geological Survey. (2023). Extension in the Rio Grande Rift. Retrieved from https://www.usgs.gov/publications/extension-rio-grande-rift