EXCERPTS FROM SLIDE SHOW PRESENTED AT EUNICE, NEW MEXICO Richard Hayes Phillips, Ph.D. January 29, 2007 As one heads northward from Highway 176, following the lowest possible pathway, with slightly higher land on either side, there is some evidence of surface runoff. The soil is predominantly sand, but there is noticeable clay content. As one approaches a broad swale, the vegetation becomes thicker. The mesquite bush is rather dense. The soils are conspicuously a clay surface, indicating that this depression does collect rainwater, transmitting it downward. For if this were an undrained playa, one would expect to find some evidence of an evaporite crust. As one approaches the structural depression, one sees a rather large area, 100 feet long, 30 feet wide. It is floored with desiccated clay, very large cracks. It was still moist on Saturday, January 27, 2007, when I was there. ... At times, this depression holds enough water that it has some overflow areas (measuring) about 30 feet by 25 feet. Surface water flows into this depression from more than one direction. ... This is a closed topographic depression underlain by structural depressions observable in the structural contours of both the caliche and the underlying Triassic red beds. There is no evaporite crust as might be expected in an undrained playa. This is a sink hole, a recharge point for the underlying aquifers. Water was encountered in boreholes both above and below this depression, at 38 feet below the surface above it, and at 212 feet below the surface below it, indicating that water may find its way through open fractures in the underlying red beds and into deeper levels, as has been observed elsewhere in southeastern New Mexico.As one continues northward along that drainage course, one sees that five tunnels had to be constructed underneath the railroad bed to accommodate the surface runoff in times of flooding. ... As one continues northward toward Baker Spring, one is now walking downhill out of the catchment of the structural depression that I showed you earlier. This is a water course flowing northward toward Baker Spring, which is at the base of the caliche escarpment in the background. As one continues northward, the water course becomes more and more incised, more well defined. Here it has actually undercut the bank. Here you see a clast of caliche with solution features in it. This is characteristic of a karst region where fresh rainwater has dissolved and enlarged small holes in the caliche. ... In some places we have what geomorphologists call desert pavement, where all that is left are the pebbles that were included within the caliche when it was first cemented. And now that the surrounding matrix has been dissolved away, one is left with a floor of pebbles, well rounded, many different colors, many of them chert, characteristic of the Antlers Formation, but also found in lesser quantities in the Ogallala Formation. ... Continuing northward along the sometimes dry, sometimes wet water course toward Baker Spring, you see the vegetation thickening. There is the caliche escarpment beneath which Baker Spring is located. As one moves farther north, there it is. There is Baker Spring. And these, ladies and gentlemen, are caves. ... Baker Spring obviously holds a lot of water, in contrast to the structural depression I showed you earlier, which holds water on an ephemeral basis, accounting for the clay floor, but it ultimately infiltrates into the ground. You see here where solution of caliche is undercutting the caprock, which will eventually break off. ... The walls of this cave are not even rock. This is silt with chert pebbles in it: pink, very poorly consolidated silt. It is very difficult to obtain a sample of this without it crumbling in your hand. ... These caves, being not in limestone or in gypsum but in soft, unconsolidated sediments underlying the caprock, will not last for long, from the standpoint of geologic time. This is precisely the sort of solution activity that undercuts the caprock in caliche areas and causes the caprock to collapse causes the scarps to retreat. These two sites, the WCS site and the LES site, are not just near a karst region. They are in a karst region.
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