Teepee Canyon ("Hell's Canyon"), Custer Co., South Dakota, USA
|Latitude & Longitude (WGS84):||43° 43' 58'' North , 103° 53' 18'' West|
|Latitude & Longitude (decimal):||43.73278,-103.88833|
|Köppen climate type:||Dfb : Warm-summer humid continental climate|
Teepee Canyon is located on the north side of Highway 16, about 18 miles west of the town of Custer, South Dakota. Two main areas (West Tepee Canyon & Sawmill Spring [FS Road#456] area) about 1-2 miles west of the Jewel Cave monument boundary are where the main diggings are located. Agates occur within small to large, tan to chocolate colored chert nodules in limestone and dolomite of the lower Minnelusa formation. Most nodules are plain and devoid of fortification agate, or have plain red jasper. It is said that any nodule containing more than 25-30% agate is rare. The gem-quality agates display fine fortification banding with alternating layers of red, black, orange, yellow, pink, cream, and white. The centers of the agates typically contain calcite (common) or drusy quartz and (more rarely) amethyst. The finest specimens display the trademark "holly leaf" fortification pattern. The main deposits at Tepee Canyon were covered by active mining claims for many decades which ultimately expired or were forfeited in the mid to late 1980's-1990's; a large fire devastated the Tepee Canyon and surrounding areas about 2000; Between the fire and mid-August 2012, a portion of the Tepee Canyon area was closed (withdrawn) to new mining claim locations and during that time since all prior valid claims had expired, the nodules could only be collected by hand digging from existing surface exposures and existing workings per U.S. Forest Service regulations. In mid-to-late August 2012, part of the withdrawl order for the Teepee Canyon area expired, and since the expiration of the withdrawl at least four (4) new mining claims were staked on the existing workings and deposits. The area known as "Hells Canyon" is still closed to collecting as it is part of Jewel Cave Monument. The collecting and breaking of the agate nodules from the tough limestone matrix is hardrock mining. The further one extends out from the traditional Tepee Canyon sites, the agates show duller tones and banding, although newer surface deposits with colorful agate have been found since the fire.
It is now generally accepted & proven that the famous "Fairburn" agates (found in gravels on the plains and grasslands east of the Black Hills) actually originated in the bedrock at Tepee Canyon and other Black Hills area locations.
In early literature, agates from this locality were sometimes referred to as "Hell's Canyon agates."
Mineral ListMineral list contains entries from the region specified including sub-localities
2 valid minerals.
This geological map and associated information on rock units at or nearby to the coordinates given for this locality is based on relatively small scale geological maps provided by various national Geological Surveys. This does not necessarily represent the complete geology at this locality but it gives a background for the region in which it is found.
Click on geological units on the map for more information. Click here to view full-screen map on Macrostrat.org
|Early Permian - Pennsylvanian|
272.3 - 323.2 Ma
|Minnelusa Formation, undivided|
Age: Paleozoic (272.3 - 323.2 Ma)
Reference: Redden, J.A., E. DeWitt. Maps Showing Geology, Structure, and Geophysics of the Central Black Hills, South Dakota. U.S. Geological Survey Scientific Investigations Map 2777. 
|Cisuralian - Late Pennsylvanian|
272.3 - 303.7 Ma
Age: Paleozoic (272.3 - 303.7 Ma)
Stratigraphic Name: Minnelusa Formation
Description: Variegated, yellow to red, gray to brown, pink to purple, and black, interbedded sandstone, siltstone, shale, limestone, dolomite, calcarenite, chert and brecciated beds. Thickness 394-1,175 ft (120-358 m).
Reference: Horton, J.D., C.A. San Juan, and D.B. Stoeser. The State Geologic Map Compilation (SGMC) geodatabase of the conterminous United States. doi: 10.3133/ds1052. U.S. Geological Survey Data Series 1052. 
Localities in this Region
- South Dakota
- Custer Co.