Day 2 : Stop 5

DAY 2 (9/27/2025) - STOP 5

"Rattlesnake Springs"

COORDINATES: 32.11153° N, 104.46667° W

Fig. 16 Rattlesnake Springs Landscape

     The next site we visited was Rattlesnake Springs (fig. 16) at the base of the Guadalupe Mountains, where the uplifted Capitan Reef forms the dominant aquifer that feeds the spring. Although the surrounding landscape is dry and semi-arid, the spring remains perennial because its water originates far upslope within the porous carbonate units of the ancient reef complex. Rainfall and snowmelt enter the exposed limestone at higher elevations, moving downward through pores, fractures, and karstic conduits that developed as the Capitan limestones dissolved over time. This allows water to accumulate within the aquifer, meaning that even in prolonged droughts, the spring still has water. 

    As the water moves through the carbonate rocks of the reef, it becomes rich in dissolved bicarbonate and calcium. The interaction between acidic meteoric water and the carbonate bedrock leads to dissolution, which enhances the porosity of the reef and produces a conduit system that supplies the spring. By the time this water emerges at Rattlesnake Springs, it is often supersaturated with respect to calcium carbonate. Upon reaching the surface, physical and chemical changes, such as degassing or evaporation, promote carbonate precipitation. 

    Also abundant at this spring are photosynthetic material, especially green algae, that thrive in the bicarbonate-rich water. Although this is a freshwater environment, the presence and role of these algae allude to shallow-marine carbonate factories discussed in class. In marine systems, organisms such as Halimeda (fig. 17) and other calcareous green algae incorporate calcium carbonate into their skeletal structures during life. When they die, their carbonate-rich fragments accumulate on the seafloor, contributing to sediment production and reef growth. At Rattlesnake Springs, the algae do not build skeletal carbonate in the same way, yet they still interact with the supersaturated water by using dissolved bicarbonate during photosynthesis. 

    Where conditions favor precipitation, calcium carbonate settles onto the substrate, forming small accumulations that, given enough time and stability, could develop into tufa or travertine. Overall, the spring captures the relationships of biological influence, carbonate supersaturation, and hydrologic forcing similar to ancient carbonate deposition. Standing at the spring, we can imagine how similar interactions operated across wide areas of the Permian Delaware Basin, where light, warm water, and abundant photosynthetic organisms produced the framework of the Capitan Reef.

Fig. 17 Green Algae - Halimeda