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

PURPOSE AND SCOPE OF THE INVESTIGATION

In cooperation with the National Park Service, an investigation was made of the surface geology and groundwater resources at Jewel Cave National Monument near Custer, S. Dak. The purpose of the investigation was to locate additional supplies of water and to determine the geologic source of the present water supply.

This report summarizes the surface geology and the lithology and water-bearing characteristics of the strata penetrated by drilling a test well during the investigation. The test well provides the only subsurface information available in the vicinity of Jewel Cave National Monument and is the only test well referred to in this report.

PREVIOUS INVESTIGATIONS

No previous detailed investigation has been made of the geology at Jewel Gave National Monument. Darton (1918, p. 53-60) discussed the general stratigraphy of the southern Black Hills region and described the artesian water supplies obtained in the foothills 15 to 30 miles south of Jewel Cave. Some of the wells listed by Darton obtained water from a sandstone of Cambrian age that underlies Jewel Cave National Monument. A more detailed stratigraphic and structural study of the region was made in 1925 and the faulting near Jewel Cave was briefly described by Darton and Paige (1925, p. 18).

METHODS AND PROCEDURES

The test well was drilled by a standard cable-tool drilling rig under a contract issued by the National Park Service. Samples of the cuttings were taken at 5-foot intervals. The samples were washed, dried, and carefully examined with a binocular microscope for such features as grain size, crystallinity, porosity, and color.

A weighted steel tape was used to make frequent checks on the drilling depth of the well. All depth measurements cited herein, whether to the water level or to different rock strata, are given in feet below land surface. Altitude of the land surface at the test hole is about 5,340 feet above mean sea level.

Estimates of thicknesses of formations at the test-well site were based upon calculations made from dip readings taken at the outcrop area 6 miles east of the monument.

LOCATION, AREA, AND EXISTING FACILITIES

Jewel Cave National Monument is in Custer County, S. Dak. about 12 miles southwest of the city of Custer and 9 miles east of the South Dakota-Wyoming State line. Boundaries of the monument enclose a rectangular area of 2 square miles; the longest dimension is 2 miles in an east-west direction. Jewel Cave and the test well are near the southeast corner of the monument.

Facilities at Jewel Cave in 1959 consisted of one small log building, a small parking lot, and a campground. The log building was used as a headquarters and as temporary lodging for the rangers who are seasonally employed as guides for tours of the cave.

PRESENT WATER SUPPLY

The water-distribution system at the cave site includes a drinking fountain, sink, shower, and restrooms at the headquarters building and a single faucet at the campground where campers may obtain water for cooking and drinking. These outlets are supplied from a buried concrete reservoir about 100 feet north and 15 feet higher than the headquarters building. The single line from the reservoir extends directly to the headquarters building and a branch line from the headquarters building supplies the campground outlet about 300 feet east.

Water to be stored in the reservoir is collected at a small spring (NW1/4NE1/4NE1/4 sec. 2, T. 4 S., R. 2 E.) about 1,500 feet northeast of the headquarters building and is transported to the reservoir by gravity flow through a 2-inch galvanized pipe. Yield of the spring varies but the average yield during the summer is estimated to be 2 gpm.

Generally, the total water consumption ranges from 1,000 to 1,500 gpd (gallons per day) but on days when the number of visitors is unusually large (200 or more), the 3,000-gallon reservoir is frequently depleted. As the spring is the only source of water for visitors, campers, and maintenance personnel, the water supply is often inadequate.