USGS Logo Geological Survey Professional Paper 65
Geology and Water Resources of the Northern Portion of the Black Hills and Adjoining Regions in South Dakota and Wyoming


The principal mineral resource of the northern Black Hills is gold, which is produced to a value of more than $5,000,000 a year. It is not, however, the purpose of this report to describe the metallic minerals of the region, for they are treated in other publications.a

aIrving, J. D. Emmons, S. F., and Jaggar, T. A., Jr., Economic resources of the northern Black Hills: Prof. Paper U. S. Geol. Survey, No. 26, 1904. O'Harra, C. C., Mineral wealth of the Black Hills: Bull, South Dakota School of Mines, No. 6, and Bull. No. 3, South Dakota Geol. Survey, 1902.

Details regarding gold in the Nigger Hill and Bear Lodge uplifts and tin near Bear Gulch are given in the Sundance folio, by N. H. Darton.b

bSundance folio (No. 127): Geologic Atlas U.S., U. S. Geol. Survey, 1905.


In the basal portion of the Lakota sandstone there are local deposits of coal, a northward extension of those in the Cambria coal field. The deposits are not continuous, and they thicken and thin irregularly. Owing to the talus of sandstone blocks, which accumulates on the slopes along the Lakota-Morrison outcrop, it is difficult to explore the coal horizon. The outcrop line of that horizon is shown on the map (Pl. IV), but only at a few points is it bare of talus and at some of these localities coal may have weathered or burned out and the sandstone roof closed down.

At Aladdin deposits of coal in the lower portion of the Lakota formation are worked to a considerable extent. A branch railroad extends from the mines down Hay Creek to connect with the Chicago and Northwestern Railway near Belle Fourche. The shipments in 1902 amounted to about 10,000 long tons, and the product is a good soft bituminous coal, suitable for locomotive and, domestic use. The principal basin lies along and north of Hay Creek, and the good coal thins and merges into more impure beds laterally. Two principal beds are worked, a lower 3 to 5 feet thick and an upper 2 feet thick, the two being separated by about 10 to 20 feet of sandy shales. The deposits are broken by a number of small faults which add greatly to the difficulty of mining. The mines comprise four openings in the lower slope of the ridge on the north side of the Hay Creek valley at Aladdin. They begin at the coal outcrop under a steep cliff of Lakota sandstone, and two of them extend northward for nearly a quarter of a mile along the coal beds, which dip very gently to the northeast. One small opening is on the upper coal bed at a point where it is about 2-1/2 feet thick, but it is usually thinner. The principal workings are on the lower bed, which is from 2-1/2 to slightly more than 3-1/2 feet thick in the mines. In one of the earlier mines a thickness of 6 feet was found at one point. The coal basin appears to extend over an area of considerable size about Hay Creek, and numerous prospect holes show extensive beds of pure coal which in most portions of the area are only a foot or less in thickness. It is possible that other basins may be found in adjoining regions, for the coal horizon is above ground all along both sides of the Bear Lodge Mountains north of the head of Redwater Creek, in the basins of Pine, Oak, Deep, Hay, and North Redwater creeks, and on the slopes on the south side of Medicine Creek. At a number of localities, however, there are exposures of an apparently complete section of basal Lakota beds down to the Morrison contact, showing little or no trace of coal, probably indicating that if coal beds are present west and north of the Hay Creek basin they are of small extent.

Coal has been mined to some extent for local use 1-1/2 miles southeast of Holwell's ranch and at several localities west of Sundance. Recently some openings have been made 3 miles west of Inyankara Mountain, exposing a small deposit. The main opening southeast of Holwell's is in the SE. 1/4 sec. 31, T. 48 N., R. 62 W., where there is an adit about 55 feet long. The coal is 8-1/2 feet thick, comprising 5 feet of hard pure coal, about 2 feet of pure, very hard coal which is particularly valuable for blacksmith's use, and at the base 1-1/2 feet of bone merging into cannel coal. The upper coal contains considerable sulphur, an ingredient of infrequent occurrence in the lower bed. Over the coal are about 2 feet of sandy shales overlain by hard sandstone, which makes a good roof. The floor is sandstone of the basal bed of the Lakota formation. The bone burns well but leaves a large amount of white ash and slacks readily. The dip, which is to the southwest, is very gentle. About 60 feet above the main deposit is a bed varying from 1-1/2 feet to 3 feet in thickness, consisting of a mixture of clay, sand, and coal, too impure for fuel. The following analyses of the coals of the main bed have been furnished through the kindness of Mr. George Bidwell, of the Chicago and Northwestern Railway Company:

Analyses of coals southeast of Holwell's ranch, Wyoming.

From large
From small
shale parting.

Volatile matter39.5141.1630.85
Fixed carbon41.8740.3725.69




In the same quarter section, but about 500 feet farther west, is another tunnel 100 feet long on the main coal bed, which is here 6-1/2 feet thick and contains but little bony deposit near its bottom. The coal is very firm and of excellent quality. It is overlain by 3 feet of light-colored sandy clay, capped by a thick mass of smooth, uniform sandstone which forms a good roof. The floor is a very hard sandstone, as in the other mine. Two miles to the southwest, in Sec. 12, T. 47 N., R. 63 W., near the north line of the northwest quarter, is another tunnel 100 feet long. The same bed is exposed here and is about 4 feet 4 inches thick, nearly all pure coal of more than usual hardness. The roof at this place is sandstone without the intervening shale. West of Holwell's ranch, on the west side of Skull Creek, coal has been found at one or two points at the base of the sandstone cliffs; its thickness and extent have not been ascertained, but apparently the deposit in this locality is of diminished thickness.

It is reported that on the ridge west of Inyankara Mountain the coaly deposit near the base of the Lakota formation has a thickness of 9 feet, but is mostly shale and bone. West of Sundance the principal mine exposes a coal bed of excellent quality, somewhat over 4 feet in thickness.


The Spearfish formation carries deposits of gypsum—a hydrous sulphate of lime—throughout its extent, and the mineral occurs in beds sufficiently thick and pure to be of value if near to market. When gypsum is calcined at a moderate heat to drive off the greater portion of the chemically combined water and is then ground, the product is plaster of Paris. The two principal beds of gypsum are in the upper and lower portions of the formation. The upper bed is thickest in the ridges east of Spearfish, where it is 18 to 20 feet thick, and in Oil Creek valley and about Red Butte, where it is 25 feet thick. It is 10 feet thick near Sturgis, 6 to 8 feet near Whitewood, and 4 feet near Sundance. The lower bed, which occurs about 120 feet above the bottom of the formation, is prominent in the Sundance region and in Government and Redwater valleys, where it is 10 to 25 feet thick. Farther east and south it is only about 5 feet thick. The gypsum is mostly pure white or light gray in color, massive in structure, and nearly pure. It has been worked to some extent at Sturgis, but the distance from market has proved too great to make the industry profitable.


Small amounts of petroleum occur in some of the sandstones surrounding the Black Hills, but so far no evidence has been obtained that a large supply is available. Wells have been sunk at various localities without encouraging results. The best prospects in the northern region appear to be in the Moorcroft field, 15 miles northeast of Moorcroft, where there are several small seeps of oil from the lower sandstone of the Graneros formation and where several exploratory wells have been sunk. One of these, 306 feet deep, is reported to have yielded 5 barrels a day for a while. Other deeper wells obtained no satisfactory supply and some of them were sunk in such manner that they could not possibly reach the oil sand. Two of the borings, 800 and 1,300 feet deep, were bored on the south side of Belle Fourche River. The locations of the springs and wells in this field are shown in figure 13. Queen City wells Nos. 1 and 2 and Northwestern No. 2 obtained a small amount of oil, but the others shown on the map obtained more.

FIGURE 13.—Map of oil field northeast of Moorcroft, Wyo. By W. C. Knight.

Wells about Belle Fourche and Sturgis and at Jerome and Thornton penetrate the Dakota and associated sandstones, but have found no trace of oil. A large amount of "oil land" has been taken up in the Piney Ridge—Wind Creek district, but it presents no good prospects of oil.


Bentonite is a hydrous silicate of alumina with some other components in small proportions. It is valuable on account of its high absorbent qualities, having the capacity for absorbing three times its weight or about seven times its volume of water. It occurs in greatest abundance in the southwestern portion of the area treated in this report and has been mined to some extent at a point 3-1/2 miles northwest of Osage, or 6 miles southeast of Jerome, on the east side of the railroad track. The material is a light-gray, fine-textured, soft, massive stone, but at the surface it weathers to a light powdery substance resembling white corn meal. Near Osage, where the bed is about 4 feet thick, it occurs in Graneros shale of so low a dip that the deposit is exposed over a considerable area. The mineral has been used with success as a soap filler and also in the manufacture of paper, but it has proved most valuable for a packing for horses' hoofs and as a diluent for certain powerful drugs in powdered form. An analysis made by the Wyoming State School of Mines is as follows:

Analysis of bentonite.

Iron oxide3.70
Sulphuric acid1.58


The extensive exposures of Pahasapa Whitewood, and Minnekahta limestones afford an unlimited supply of rock for burning into lime or for flux. The Whitewood limestone has been extensively quarried for the latter purpose 2 miles below Deadwood (see Pl. VI, B), and the product utilized in the smelter near by.


The extensive deposits of limestone and shale occurring close together in the Black Hills uplift afford suitable material for cement at many localities and doubtless will be utilized for this purpose when there is sufficient demand. Portions of the Niobrara formation appear to consist of carbonate of lime and clay in proper proportions for the direct manufacture of cement, but no test of the material has yet been made. The cement at Yankton, S. Dak., is manufactured from Niobrara chalky limestone mixed with the overlying Pierre shale.


Portions of the Fuson formation are suitable for fire clay, and this material has been mined for that purpose to some extent in pits 2 miles south of Rapid. The product has proved very satisfactory for the manufacture of fire brick, which have been shipped in moderate numbers to various places. An upper bed of the Unkpapa sandstone has also been worked for fire clay on the north side of Rapid Creek near the reservoir, but the pit was finally abandoned. The deposits in the Fuson formation are somewhat variable in character, some portions being refractory while others could not be used. The following analyses were made by R. A. Slagle at the School of Mines at Rapid:

Analyses of fire clays from near Rapid, S. Dak.

SiO287.0583.30 76.7881.98
Al2O36.5612.30 14.4313.08
Fe2O3.64.80 .18.21
CO2.951.30 2.181.46
MgO1.24Trace. .95.31
Alkalies3.01--- Trace.Trace.
Loss on ignition1.80--- 4.624.07





Nos. 1 and 2 are varieties tried at an earlier stage of experimentation. No. 3 is from middle Fuson beds on the east slope of the ridge, and has given the best results. No. 4 is from Rocker ville Hill; the upper softer part of it is serviceable for cementing the harder varieties.


The Black Hills have a climate much more attractive than that of the adjoining plains. The extremes of temperature are less, both diurnally and annually, and the precipitation is more abundant. The weather is dry and hot in summer, moderately moist in late spring, and cold, with moderate snowfall, in winter. The climatic features vary from year to year, and show much local variation from point to point, particularly in rainfall. More snow falls in the Black Hills than on the adjoining plains, and, owing to the greater shade and shelter from sun and wind, it remains longer on the ground. Records of the weather at various points in the hills and their vicinity have been kept for many years, and from these the diagrams constituting Plates XXIII and XXIV and figures 14 and 15 have been compiled. Much information up to the end of the year 1891 was obtained from the report by Lieut. John P. Finley.a Plate XXIII and figure 14 illustrate the local and annual variations in temperature from month to month at points in or near the Black Hills. The prominent feature is a gradual rise of temperature in the spring to a maximum in July and August, as in most places on the same latitude. These two months often have an average of 70°, generally being a little more on the plains and somewhat less in the woods and on the high lands. Ordinarily July is hotter than August. The temperature has a great range in the twenty-four hours in summer, often rising considerably above 100° in midday and falling below 60° at night. In the autumn there is a gradual decline in temperature for the first two months, and then usually a rapid fall to uniformly low temperature, which prevails throughout December and January. The average winter temperature is usually between 20° and 25°, but it varies more or less. As shown in figure 14, the mean annual temperature varies considerably both in different localities and from year to year. It is considerably lower in the northern part of the Black Hills, probably owing entirely to the difference of latitude.

aCertain climatic features of the two Dakotas, U. S. Weather Bureau, 1893, 204 pages.

FIGURE 14.—Diagram of mean annual temperature in the Black Hills region.

FIGURE 15.—Diagram of total precipitation in the Black Hills region.

PLATE XXIII.—DIAGRAM OF TEMPERATURES IN THE BLACK HILLS AND ADJOINING REGIONS, 1879-1899. By months, January to December. Space between two parallel lines represents 20 degrees. (click on image for a PDF version)

PLATE XXIV.—DIAGRAM OF RAINFALL IN THE BLACK HILLS AND ADJOINING REGIONS, 1878-1899. By months, January to December. Space between two parallel lines represents 2 inches. (click on image for a PDF version)

The Black Hills exhibit a higher average temperature in winter and a lower average in summer than the adjoining plains. The explanation that has been offered for this difference is the fact that the region is protected by heavy forests from the high and dry cold winds which sweep across the plains.

The normal monthly temperatures for typical northern Black Hills stations up to the end of 1891 were as follows:

Normal monthly temperatures in the Black Hills.


Fort Meade182131445465717059483324

The average number of days in which the maximum temperature equaled or exceeded 90° were, at Fort Meade, about two days in June, seven days in July, seven days in August, one day in September; at Deadwood, less than one day in June, two days in July, and one day in August.

Precipitation in and about the hills is extremely variable, much of the variation being local. The rainy season in the spring, which in some years attains its culmination in May and in others in June, is usually followed by a period of drought in July, and generally there are numerous scattered showers in August and September. Snow is usually expected early in October, but the first snows are light and do not lie long on the ground. The midsummer precipitation in the Black Hills is not large in volume, but scarcely a day passes without light local showers at one point or another. They usually fall out of small clouds moving in narrow zones, and are a very small factor in agriculture. The rain often falls from one stratum of air and is absorbed again in another before so reaching the ground. The idea that the climate of the region is changing—a theory which many people hold—is not borne out by the meteorological records. The great variation from month to month and from place to place seems to recur through recent seasons with the same range and averages shown in the earlier records. The average number of rainy days in which the precipitation at Deadwood and Rapid equaled or exceeded 0.01 inch is as follows:

Rainy days on which precipitation at Deadwood and Rapid, S. Dak., equaled or exceeded 0.01 inch.



The average number of clear days per month, or those in which less than one-third of the sky was obscured by clouds, at the same localities, are as follows:

Average number of clear days per month at Deadwood and Rapid, S. Dak.


Deadwood 129108 9111516 18151411
Rapid 136610 6699 14111413

At Deadwood the mean annual precipitation from 1878 to 1887 was 28.4 inches. At Rapid it was 18-1/2 inches from 1881 to 1891, and 16-1/2 inches from 1892 to 1906. The following excessive precipitation has been recorded:

Excessive precipitation at points in the Black Hills, South Dakota.


May 1-31, 188310
June 7, 1888 (in 12 minutes).27
August 10, 1890 (in 1 hour and 6 minutes)1.17
July 5, 1891 (in 43 hours)1.33

July 27, 1872 (in 45 minutes)1.16
August 8, 1875 (in 1 hour and 5 minutes)1.7
April 16, 18772.52
April 17, 18783.20
April 21-22, 18792.86
April 22-23, 18863.32
May 2, 18744.55
May 7-8, 18823.33
May 17-18, 18832.77
May 18-19, 18882.62
June 9-10, 18742.51
June 23-24, 18833.34
October 15-16, 18793.47

July 1, 1888 (in 1 hour)1.40
July 11, 1889 (in 35 minutes)1.40
June 4-5, 18903.8

June 14, 1891 (in 2 hours and 40 minutes)3

The average quarterly precipitation for three points in the Black Hills is as follows:

Average quarterly precipitation at Deadwood, Fort Meade, and Rapid, S. Dak.

Deadwood.Fort Meade. Rapid.

Inches. Inches. Inches.
January, February, March 4.452.422.44
April, May, June 13.559.6110.24
July, August, September 6.134.924.46
October, November, December 4.351.623.30

This precipitation, apportioned between the dry season, or winter, comprising January, February, November, and December, and the wet season, from March to October, inclusive, is as follows:

Average precipitation during wet and dry seasons at Deadwood, Fort Meade, and Rapid, S. Dak.

Locality.Dry season.Wet season.

Inches. Inches.
Fort Meade2.3016.27

The average monthly precipitation at these three places, deduced from observations to the end of 1891, is as follows:

Average monthly rainfall at Deadwood, Fort Meade, and Rapid, S. Dak.

Locality. Jan.Feb.Mar.Apr.May.June. July.Aug.Sept.Oct.Nov.Dec. Annual.

Deadwood1.251.211.99 5.174.653.732.84 1.5128.48
Fort Meade.73.631.07 2.384.023.222.40 .4618.59
Rapid.45.831.16 2.034.303.912.14 .4518.46

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Last Updated: 24-Aug-2009