Proceedings of the South Dakota Academy of Sciences, vol. 73, p. 279 (1994).

A bison mass death site at Krogman Ranch,
Mellette County, South Dakota

Timothy H. Heaton and Gary D. Johnson
Department of Earth Sciences
University of South Dakota
Vermillion, SD 57069

A mass death site of Bison bison has been found northeast of the town of White River and is being excavated by an interdisciplinary group of professors and students from the University of South Dakota. The bones are currently being prepared for display at the W. H. Over Museum in Vermillion.

The bone deposit is located along a receding bluff of the White River Group and is covered by White River slump debris. The location of the deposit at the top of a small knoll indicates that much slope retreat has taken place since burial. Two radiocarbon dates on the bone gave ages of 1,925 +/- 70 years B.P. (AA-11513) and 2,010 +/- 60 years B.P. (AA-11512).

The deposit covers an area of at least 5 m by 3 m with a 10 degree slope down the long axis. The highest part of the deposit, nearest the bluff, is thickest (1 m), most concentrated in bone, and has the most distinct boundary. Articulated individuals are covered by a dense tangle of disarticulated elements. Bone concentration and deposit thickness decrease rapidly down slope.

So far about a thousand bones have been recovered, plus the contents of several blocks removed in plaster jackets to preserve skulls. A field count of 24 tibias (adult and juvenile) gives a minimum number of individuals (MNI) of 12. All skeletal elements are represented, and no evidence has been found to suggest human intervention or modification. The only non-bison animal found is a gopher (Thomomys sp., 2 lower jaws) from high in the deposit.

This locality does not seem to represent any kind of long-term natural trap, so death for all bison was probably simultaneous. The younger radiocarbon date is from a deeper element in the deposit than the older one. Possible modes of death are 1) a stampede off the bluff, and 2) the collapse of an overhang sheltering the animals. Some natural scattering of bones occurred after death, but eventually slump debris covered the entire deposit.

Heaton, T. H., Johnson, G. D. 1994. A bison mass death site at Krogman Ranch, Mellette County, South Dakota. Proceedings of the South Dakota Academy of Science, vol. 73, p. 279.

Timothy H. Heaton: E-mail, Home page, Phone (605) 677-6122, FAX (605) 677-6121