 Joseph C. Brown surveyed the boundary according to the description found in the Missouri State Constitution of 1820, which said the northern border of the state began at rapids on the Des Moines River.Brown found a set of small rapids near present-day Keosauqua, Iowa, and ran the border due west from that point.In 1838, the Missouri Legislature passed a law declaring this line its northern boundary, essentially seizing nearly of land from the Iowa Territory.