Edit to add: more likely a phalange
This was found in the river at the confluence of the Blue Earth and Minnesota River in South Central Minnesota on August 3, 2018. It appears to me to be an astragalus, the size of that of a white tailed deer, but the shape is not quite right.
It matches none of the astragali found in Miles Gilbert's Mammalian Osteology.
The "bump" at about the 4cm mark in two of the photos seems like a very distinctive feature, yet I cannot find an identification for this.
About our area:
This area was, in early American times, the land of the Sioux Indians and the bison. Geologically, this area is very rich in silica. We find a lot of mineralized bones of bison, bos, Odocoileus virginianus, etc. This is the north eastern edge of the great plains.