In 1955, when I-35 was still just plans, workers were excavating a sewer in the Trout Brook valley near the intersection of Mississippi Street and Maryland Avenue. Today, Mississippi no longer intersects with Maryland; this is instead approximately where I-35E is crossed by Maryland. At about 14 ft (4.3 m) below the surface, the workers found a variety of fossils in a thin marl within a peat bed, among them three bison skulls thought to be in the neighborhood of 8,000 years old. No doubt the skulls were the most visually impressive finds, but conifer and deciduous pollen, sedge seeds, and freshwater snails were also found. The microfossils indicate that the local environment was similar to the present, with pine, oak, and elm trees, but not a dense forest (Rowley 1960). The depositional site itself appears to have been a blocked glacial channel that had turned into a bog by the time of the bison (the Twin Cities, of course, being just lousy with buried former channels) (Taylor 1960).
The bison remains belong to the extinct species Bison occidentalis. Modern bison remains were found higher in the section. Bison bones in general have been commonly found in the buried peat of the metro. There can be a bone per square foot in the densest concentrations. Peat itself is common in the subsurface, and can be quite thick: up to 85 ft (26 m) in places (Taylor 1960).
|Bison occidentalis as restored in Hay (1913) from a museum specimen.|
Hay, O. P. 1913. The extinct bisons of North America, with description of one new species, Bison regius. Proceedings of the United States National Museum 46:161–200.
Rowley, J. 1960. A preliminary pollen study from a fossil bison site in Saint Paul. Minnesota. Proceedings of the Minnesota Academy of Science 25–26:40–50.
Taylor, P. S. 1960. A report on fossil bison from a peat bog in Saint Paul, Minnesota. Proceedings of the Minnesota Academy of Science 25–26:200–203.