Day 3 : Stop 1

DAY 3 (9/28/2025) - STOP 1

"Bottomless Lakes State Park"

COORDINATES: 33.33846° N, 104.33444° W

*Also Stop 1 of Day 5*

Fig. 19 Bottomless Lake Landscape

  Our next stop was the Bottomless Lakes State Park (fig. 19), a site characterized by evaporite karst processes and active groundwater discharge. The park lies along the eastern margin of the Pecos River valley, where a series of deep, steep-walled sinkhole lakes formed through dissolution and collapse within the Permian Artesia Group. These rocks, consisting of interbedded gypsum (fig. 20), mudstone, limestone, and lesser sandstone, represent the far back-reef equivalent of the Capitan Reef complex exposed farther south in the Guadalupe Mountains (Land, 2003). Their composition and solubility make the region susceptible to subsurface dissolution and subsequent collapse, producing the distinctive morphology of the Bottomless Lakes. 

    Groundwater rising from the underlying San Andres artesian aquifer dissolves gypsum and halite as it moves upward, generating cavernous voids and breccias. Over time, the collapse propagates toward the surface, forming circular sinkholes up to 100 meters in diameter and 30–60 meters deep. Many lakes within the park, such as Lea Lake and Lazy Lagoon, consist of multiple coalesced collapse features, and several display steeply dipping or sagging beds along their margins, evidence of continued subsurface dissolution and mass wasting (McLemore, 1999). The steep walls, joint-aligned configurations, and compound lake basins show that these structures have evolved through repeated cycles of dissolution, collapse, and stabilization.

Fig. 20 Gypsum Beds in Seven Rivers Formation

    The rocks exposed around the sinkholes are primarily gypsum and mudstone of the Seven Rivers Formation, a unit within the Artesia Group that makes up the bluffs bordering the park. These evaporite-rich units record deposition along the Permian shelf (fig. 21), where restricted marine conditions produced alternating beds of gypsum, red beds, and thin carbonates. As the Delaware Basin subsided and circulation became restricted, salinity fluctuated, allowing thick gypsum layers to accumulate. Today, these evaporites are integral to karst development. The dissolution of gypsum is rapid compared to limestone, resulting in vertical-walled cenotes and unstable escarpments prone to collapse. Features such as sagging strata above Cottonwood Lake and tilted beds near Lea Lake directly reflect recent dissolution and differential subsidence of these evaporitic units (McLemore, 1999).

    Hydrologically, the Bottomless Lakes function as discharge points for the San Andres artesian aquifer. The cenotes are sustained not by surface inflow but by upward-moving groundwater, an unusual phenomenon in an arid region where evaporation exceeds precipitation. Springs that emerge along the lake floors consist of brackish or saline water enriched in sulfate and chloride due to its passage through subsurface gypsum and halite. Long-term measurements show fluctuations in lake levels that correspond to artesian aquifer pressures rather than seasonal rainfall, proving the dominance of groundwater in sustaining these water bodies (Land, 2003). The salinity between lakes also shows local variations in the flow paths and mineral content of groundwater entering each sinkhole.

    From a sedimentary and stratigraphic perspective, the Bottomless Lakes provide a view into the interactions between Permian depositional systems, post-depositional diagenesis, and modern hydrologic processes. The Artesia Group records shallow-marine to sabkha environments on the Permian shelf, while present-day sinkholes reveal how evaporite sequences respond to groundwater circulation over geologic time. The cenotes themselves serve as examples of depositional basins where organic-rich sediments, evaporitic precipitates, and groundwater-derived materials accumulate, forming a sedimentary archive within karst basins.

Fig. 21 Permian Basin of New Mexico and West Texas
(Adams, 1965; Hills, 1984; Ward et al., 1986)

External References:

Land, L. (2003). Evaporite Karst and Regional Ground-Water Circulation in the Lower Pecos Valley of Southeastern New Mexico, Oklahoma Geological Survey Circular 

https://usflearn.instructure.com/courses/1985970/files/folder/Field%20trip%20materials/Bottomless%20Lake?preview=199515618

McLemore, V. (1999). Bottomless Lake, New Mexico State Park Series. https://usflearn.instructure.com/courses/1985970/files/folder/Field%20trip%20materials/Bottomless%20Lake?preview=199515554

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