Major Warren, a Civil War hero, western explorer, and respected cartographer, was an excellent choice as the first St. Paul District Engineer. He worked closely with local, State, and congressional interests to improve St. Paul as a transportation center and Minneapolis as a mill and lumber center. He designed the Mississippi River headwaters reservoirs; constructed a bridge at Rock Island; and surveyed the Mississippi, Chippewa, St. Croix, and Wisconsin Rivers. He initiated the first major Corps construction project in the Twin Cities – the preservation of the Falls of St. Anthony.