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Paper No. 11
Presentation Time: 10:45 AM


AGENBROAD, Larry, Mammoth Site of Hot Springs, South Dakota, 1800 Highway 18 Bypass, Hot Springs, SD 57747,

A large sinkhole, exposed by construction in the southern city limits of Hot Springs, SD served as a hydrologic-geologic natural trap for young, male mammoths and associated fauna. When active, the sinkhole was a conduit for thermal, artesian springs which created a pond within the collapse feature. Radiocarbon dating of bone apatite and carbonate indicate the infilling took place ca. 26,000 years BP, with an active period of ca. 300-750 years of infilling sediments and faunal remains. Excavations from 1974-2010 have produced a minimum of 59 mammoths (by tusk count), plus a giant short-faced bear, a camel, a llama, wolves and a large number of lesser vertebrates and invertebrates. Approximately 40 % of the fill remains to be excavated to the current depth of ca.12 m. Test drilling indicates a maximum depth of +20 m of fossil bearing sediment. Infilling sedimentation was derived from wall collapse and surface inflow during storm intervals. Spring effluent was eventually diverted from the sinkhole to the Fall River entrenchment, ending the active, trap. Subsequent erosion left the sinkhole deposits as a local topographic high which was being lowered by a development project. The exposure of multiple, large bones by the bulldozer led the contractor to seek professional assessment of the deposit. Testing and paleontological excavations resulted in the site being awarded National Natural Landmark status in 1980. The site continues to be an active excavation, a research institute, and an educational facility, open to the public, year-round.
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