South Dakota

Harney Peak
       7 ½’ quadrangle: Custer, SD
      Pennington County
       Black Hills National Forest, Black Elk Wilderness,
             Norbeck Wildlife Preserve
       Black Hills

Intrusive Igneous
7,242 ft (2,307 m)

Harney Peak from the north. (1988)

Harney Peak Granite at Sylvan Lake.

Bedrock: Harney Peak Granite

Middle Proterozoic (1740 Ma)

Fine- to coarse-grained granite and pegmatite. Layered, with graphic perthite alternating with finer-grained, more sodic granite. Tourmaline, biotite, garnet in addition to plagioclase, microcline, quartz and muscovite. Inliers of sillimanite schist south of the peak. Pegmatites abound in the surrounding Black Hills, some of them producing exotic minerals such as spodumene, beryl, columbite, and cassiterite. Rare elements are more abundant in pegmatites farther from the Harney Peak Granite than in those near it, apparently because volatile-rich fluids were able to migrate farther from the intrusion.

Surficial Geology: Erosion along joints in the granite has produced interestingly shaped outcrops, including an isolated pillar near the lookout tower at the summit. The pillar appears to be higher than the highpoint marker, but it is not.

Soil Series: Rock outcrop/Mocmont Complex: 40 to 80% outcrops and deep, well drained, very steep Mocmont Soil: dark, grayish-brown gravelly loam over pale brown to light yellow brown subsoil. Formed from weathered granitic rock under ponderosa pine, aspen, birch and bur oak forest.

Selected References:

  • Ensz, Edgar H., 1990, Soil Survey of Custer and Pennington Counties, Black Hills Parts, South Dakota: U.S. Soil Conservation Service.
  • Redden, J.A., J.J. Norton and R.J. McLaughlin, 1981, Geology of the Harney Peak Granite, in Rich, F.J., Editor: Geology of the Black Hills, South Dakota and Wyoming, 2d Ed., Field Trip Guidebooks, Geological Society of America Rocky Mountain Section, 1981 Annual Meeting, Rapid City, S.D., p.225-240.
  • Shearer, Chip K. and J.J. Papike, 1987, Harney Peak Granite and associated pegmatites, Black Hills, South Dakota, in Beus, Stanley S., Editor: Geological Society of America Centennial Field Guide, Volume 2, Rocky Mountain Section, p.227-232.

Other suggested sources of information:

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