Geological Survey Water-Supply Paper 1475-D Geology and Occurrence of Ground Water at Jewel Cave National Monument, South Dakota

None of the streams within the monument are perennial and the possibility of finding substantial amounts of water in the valley alluvium does not seem favorable. The alluvium consists chiefly of fragments of Pahasapa limestone, with a few scattered pieces of sandstone from the Minnelusa formation, covered by a variable thickness of red clayey soil. Maximum thickness of the alluvium is unknown but may be as much as 30 feet in Hell Canyon south of Jewel Cave

The problem of finding water at shallow depths in the alluvium in Hell Canyon is complicated by the presence of the large fault about 1,500 feet north of the cave. Effects of the fault on ground-water occurrence can be determined only by test drilling but there is a possibility that the fault intercepts water moving down the canyon from the north. If this is true, little water may be expected in the alluvium in Hell Canyon south of the fault near Jewel Cave.

Only one spring has been observed within the boundaries of the monument. The spring is well developed and the yield of about 2 gpm is believed to be the maximum yield that can be economically obtained. With very little effort, however, the spring could be maintained as a source of supply.

Three other springs were visited during the study; 1 was not flowing when visited and the other 2 had a combined yield of less than 2 gpm. These springs are too far from Jewel Cave and their yields are too low for them to be a suitable source of water supply.

The sandstone zones of the Minnelusa formation are excellent aquifers west of the monument where the formation is deeply buried. However, within the monument the thin remnants of the formation that cap the higher ridges probably contain only minor amounts of water. Near Jewel Cave on the east side of the monument, faulting combined with dissection of the formation by the Hell Canyon drainage system, has divided the formation into blocks of limited extent. It is doubtful that much water will be found in the formation near Jewel Cave.

Because the Pahasapa limestone is permeable and the upper 150 feet is cavernous, the water level in the formation is usually well below the outcrop area. West of the monument the formation is an excellent aquifer but within the monument boundaries, the extensive exposures of the formation indicate that it contains little if any water. Test drilling at Jewel Cave revealed only a small amount of water in the lower part of the Pahasapa limestone in the immediate vicinity of the cave.

The Pahasapa limestone is underlain by 40 feet of Englewood limestone. Generally the Englewood is moderately permeable but is rarely jointed or cavernous. These characteristics, and the fact that no water was found when the formation was penetrated by the test drill, indicate that the Englewood probably is not an aquifer in the vicinity of the monument.

The 10 feet of clean white sandstone immediately below the Englewood limestone and the sandstone section of the lower part of the Deadwood formation seem to offer the best possibilities for the development of permanent water supplies at the monument. Results of test drilling and bail tests indicate that the sandstone just below the Englewood limestone is the most productive aquifer penetrated.

The sandstone below the Englewood is separated from the sandstone section of the Deadwood by 115 feet of limestone, dolomite, and siltstone of the Deadwood formation. Samples obtained by test drilling indicate that 15 to 20 feet of the 65 feet of sandstone in the lower part of the Deadwood is sufficiently permeable to yield a significant amount of water. Combined yields of all the sandstones may be expected to be small and pumping lifts will undoubtedly be large.