Teepee Canyon ("Hell's Canyon"), Custer Co., South Dakota, USA
|Latitude & Longitude (WGS84):||43° 43' 58'' North , 103° 53' 18'' West|
|Latitude & Longitude (decimal):||43.7327777778, -103.888333333|
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and surrounding areas about 2000; Between the fire and mid-August 2012, a portion of the Tepee Canyon area was closed (withdrawn) to new mining claim locations and during that time since all prior valid claims had expired, the nodules could only be collected by hand digging from existing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
|Permian - Pennsylvanian252.17 - 323.2 Ma||Minnelusa Formation|
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).
|Permian - Carboniferous252.17 - 358.9 Ma||Carboniferous-Permian sedimentary rocks|
|Early Permian - Pennsylvanian272.3 - 323.2 Ma||Minnelusa Formation, undivided|
|Permian - Mississippian252.17 - 358.9 Ma||Mississippian-Permian sedimentary|
References for regional geology:
Data provided by Macrostrat.org
Garrity, C.P., and Soller, D.R.,. Database of the Geologic Map of North America: adapted from the map by J.C. Reed, Jr. and others (2005). U.S. Geological Survey Data Series 424 .
USGS compilers. State geologic map data. State Maps.
Geological Survey of Canada. Generalized geological map of the world and linked databases. doi:10.4095/195142. Open File 2915d.
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.
2 valid minerals.
Localities in this Region
- South Dakota
- Custer Co.
Clark, Roger (2009) South Dakota State Gemstone: Fairburn Agate. (Silverwind Agates, Publ., Appleton WI).
Custer County Register of Deeds (8/20/2012) Official Records of Mining Claim Locations, Custer County Courthouse, Custer, South Dakota.
Gries, John P. (1996) Roadside Geology of South Dakota (Mountain Press Publ. Co., Missoula MT)(5th Printing, 2009) p. 271.
Roberts, W.L., & Rapp, G. (1965) Mineralogy of the Black Hills (South Dakota School of Mines & Technology, Rapid City, SD); p.169.
Sinkankas, John (1997) Gemstones of North America, Vol. 3. (Geoscience Press, Tucson, AZ); p. 350.
Wentzell, Christopher (2011) Personal discussions with Black Hills, SD, area rock shop owners and collectors (August and September).
Zeitner, June C. (1998) Midwest Gem, Fossil, and Mineral Trails: Prairie States. (Gem Guides Book Co., Baldwin Park, CA); p. 34.
U.S. Dept. of the Interior, Bureau of Land Management. Mining Claim and other land status records (for the Tepee Canyon area);
U.S. Dept. of Agriculture, U.S. Forest Service. Black Hills National Forest regulations (as of August 01,2011); Custer, SD.
U.S. Dept. of Agriculture, U.S. Forest Service. Draft Environmental Assessment, Hell Canyon Maintenance Burn; September 2010. Hell Canyon Ranger District, Black Hills National Forest, Custer Co., SD. Pages 158, 160.