The St. Mary Reservoir, near Cardston in southern Alberta, was built and filled by the early 1950s. During reservoir draw downs and droughts, lake bottom sediments are exposed and quickly eroded, which has revealed a unique collection of artifacts and even trackways of now extinct megafauna like mammoth and camel.
Two particularly interesting artifacts are termed ‘eccentrics’ because their shape and significance are so unusual. Eccentrics are very rare artifacts, the shapes of which are thought to be determined more by aesthetic rather than functional reasons. Some archaeologists think that the large flintknapped stone artifacts from St. Mary Reservoir are symbolic representations of the branched “horns” of pronghorn antelope once common across the Great Plains. Others think they may have been ceremonial knives used on special occasions.
The artifacts are made of a material called Knife River Flint, which outcrops almost 800 km away in North Dakota. Surprisingly, artifacts made of Knife River Flint are relatively common in Alberta, which archaeologists suggest is evidence of high human mobility and/or wide trade networks that spanned the Great Plains. The abundance of Knife River Flint in Alberta has ebbed and flowed throughout pre-contact times and may relate to changing patterns of culture contact or movement. Knife River Flint spear heads have been found as far north as the Peace River area in northwest Alberta and near Fort McMurray in the northeast portion of the province. The occurrence of this exotic material heightens the importance and intrigue of the St. Mary Reservoir eccentrics.
Alberta archaeologists have taken great interest in Knife River Flint and have studied techniques to accurately identify the material (including the use of UV light to produce a relatively distinct reflective pattern) and dynamics of weathering called patination. Shayne Tolman, who first discovered the eccentrics, is documenting links between time of exposure and degree of patination (the white rind that coats some artifacts) on Knife River Flint. Pieces of the St. Mary eccentrics are different colours because they rested in different positions and were exposed to different chemical weathering agents over thousands of years.
Written by: Todd Kristensen (Northern Archaeologist)