Bottomless State Park, named after cowboys who believed the eight lakes were never-ending and numerous tails that describe horses and people drowning in one lake and coming out of the other or into the Gulf of Mexico or Carlsbad Caverns (McLemore, 1999). During the field experience, four stops were taken to discuss relevant geological formations and mineralogy.
Stop 1 shown in the image above is facing north at the overview lookout. Lea Lake is pictured which is a sinkhole from an artesian spring. In the west side of the image, there is landslide debris indicative of a collapse that formed the escarpment visible. The purpose of the stop was to understand how anhydrite and gypsum are precipitated during the formation of the Delaware Basin. As the Delaware Basin sank, evaporites such as gypsum and anhydrite formed during the Upper Permian (artesia group) about 230 million years ago. From the top of the outcrop, clay, shale, gypsum and anhydrite are seen as well as alluvial deposits from Pecos River (Fig. 1). Fibrous anhydrite precipitated in clay and cavity walls. Because the majority of the outcrop is composed of evaporites, which are quite soluble, there are many cavities and minor caves throughout the cliff (Fig. 2).
Figure 1. (A) Fibrous anhydrite (B) alluvial deposits from Pecos River identified from rounded sides indicative of transportation. Red color is from the iron in sandstone and clay in the region.
Figure 2. shows a small cave in the outcrop.
Stop 2 was at Lazy Lagoon which had three sinkholes that varied based on water source, biological activity, and water depth. The differences resulted in differing water chemistry causing a change in water color (Fig. 3).
Figure 3. a field sketch of the three sinkholes within the Lazy Lagoon system.
Stop 3 was near the visitor center at Cottonwood Lake. The purpose was to understand and see the difference between a cenote and a sinkhole. The cenote outcrop measured approximately 30 meters in height and formed due to a clear collapse of the cliff walls (Fig. 4). The formation intersects a water table and features evaporates from the artesia group.
Figure 4. a field sketch of the cenote. White layers are gypsum and red layers are clay/sandstone. Collapse debris is visible towards the bottom of the cenote.
Stop 4 was along a trail near the visitor center and Cottonwood Lake. The main purpose was to observe karren features, which is the formation of rills in gypsum from surface dissolution by rainfall (Fig. 5). Karren features are main evidence of water interaction because gypsum dissolves and moves vertically due to vertical water flow.
Figure 5. Karren features in gypsum. Pencil is 14-15cm for scale.
References
McLemore V.T., (1999). Bottomless Lakes. New Mexico State Park Series. 51-55.