In 1816 United States surveyor John C. Sullivan was instructed to survey a line north from the mouth for and then proceed east to the Des Moines River. In addition to being a round number, the line Indian Boundary Line (1816) also lined up in the east with the deep Des Moines Rapids on the Mississippi River just south of Fort Madison, Iowa, that was the northern end of navigation on the Mississippi and it also lined up with the westward adjusted boundary from the mouth of the Gasconade River the Sac had ceded in 1808. The land on the east side of the Des Moines River was the site of a Sac village which had not been ceded.