Day 3 : Stop 2

DAY 3 (9/28/2025) - STOP 2

"Sitting Bull Falls"

COORDINATES: 32.24519° N, 104.69691° W

Fig. 22 Map of Sitting Bull Falls

Fig. 23 Landscape of Sitting Bull Falls Featuring a Waterfall

Fig. 24 Porous Travertine

    Our next site was Sitting Bull Falls (fig. 22 & 23), located along the eastern margin of the range, with a landscape characterized by springs that emerge from fractured Permian carbonate strata as well as multiple waterfalls and pools. The geomorphology is influenced by groundwater flow paths that cut through the uplifted and faulted block of the Guadalupian reef complex. As water migrates through these highly porous limestones, it becomes enriched in dissolved calcium carbonate, eventually discharging at the surface to precipitate new deposits.

    At the falls, the dominant rock type we examined was a light-colored, highly porous calcareous tufa, the early stages of which can lithify into travertine. The rock was noticeably porous with open cavities, void spaces, and sponge-like textures caused by the rapid precipitation of calcium carbonate around mosses, microbial films, and splashing water (fig. 24). This rock is much younger than the reefal limestone exposed in the walls behind it. While the Permian limestones form massive, dense outcrops that reflect deposition in a marine reef environment, the tufa we observed is a freshwater precipitate forming under different conditions.

Fig. 25 Draped Textures Due to Mineral-Rich Water Flows

    We observed draped textures at this outcrop as well. These were caused by the movement of mineral-enriched spring water that flows across the slope, depositing thin layers of carbonate through the degassing of CO2 (fig. 25). The water-drip appearance, thin films, and stalactite-like protrusions show that carbonate precipitation is ongoing. The transition from soft tufa to more crystalline travertine is also visible at the site. As these deposits age, textures become smoother and more coherent, and the internal porosity decreases as voids are filled by secondary carbonate. The upper surfaces appeared relatively smooth, while the vertical faces were exposed to the dripping water and preserved finely banded accretionary layers. 

    The ancient Capitan reef complex formed in a warm, shallow Permian sea, whereas the deposits forming at Sitting Bull Falls represent a much more recent system formed in an arid landscape. Still, both share a carbonate composition and are controlled by the fundamental processes that control carbonate precipitation.