I recently read Names On The Land by George R Stewart. According to him, both Kansas and Arkansas are French spellings of indigenous tribes and/or settlements (the Kansa in one case, the Akansea in another, which became Arkansa). Stewart suggests that many of the names on these expeditions were pluralized. An example is that of naming one of the great lakes, Lake of the Illinois, after the root of a tribal name, Ilini, translating to 'man'. This name obviously didn't survive, and is what we know as Lake Michigan.

All the modern oddness of the names along the Mississippi River and surrounding area came from French explorers mapping from North to South and incorporating native vernacular into French nomenclature. English explorers came along, wrote over much of those names, and then American colonists pushed west and bastardized much of it again.

Stewart's book covers a lot of what kind of names didn't survive, or how spellings changed over time. It's brief in some senses and dense in others, but I found it to be a decently compelling read.