Fort Mandan Fort Mandan was the name of the encampment at which the Lewis and Clark Expedition wintered in 1804 - 1805 . The encampment was located on the Missouri River approximately twelve miles from Washburn , North Dakota , though the precise location is not known for certain and may be under the nearby river . The fort was built of cottonwood lumber cut from the riverbanks . It was triangular in shape , with high walls on all sides and a gate facing the riverbank . Storage rooms provided a safe place to keep their supplies . The Corps of Discovery started the fort on November 2 , 1804 , and remained in the area until April 7 , 1805 . They built the fort slightly down river from the five villages of the Mandan and Hidatsa nations . The winter was very cold with temperatures sometimes dipping to minus 45 degrees Fahrenheit ( - 43°C ) , but the fort provided some protection from the elements . As it was , quite a few men of the expedition suffered frostbite . Diplomacy . Captains Meriwether Lewis and William Clark spent much of the winter on diplomatic efforts with the tribes who lived near Fort Mandan . Because the expedition would establish the first official contact between the United States and several Native American nations , President Thomas Jefferson had several diplomatic goals for the captains to pursue . They were to try to establish a friendly relationship with as many tribes as possible and announce that American traders would be coming to the region . They were also to claim territorial sovereignty over the land . Because the Tetons had shown resistance to the expedition , Lewis and Clark gradually made an adjustment to these goals and decided to try forming an alliance with the Arikaras , Hidatsas , and Mandans against them . The Mandans were cautiously favorable towards allying with the United States , even going so far as to send one of their chiefs , Sheheke , back with the Expedition in 1806 to travel to Washington , D . C . , and meet with Thomas Jefferson . However they did not commit to trading with the United States at the expense of their previous trading partnerships . The Hidatsas were much more resistant to American diplomatic efforts , often avoiding even meeting with Lewis and Clark . Preparations for the spring . The Corps also spent a great deal of the winter preparing to travel again in the spring . On the journey up until Fort Mandan they had maps by previous explorers , but west of there they would enter unfamiliar territory . Therefore Clark gathered information from Sheheke about the route to the west to make a preliminary map . Also , not knowing whether they would survive to bring back the information they had gathered thus far , Lewis and Clark compiled their descriptions of tributaries of the Missouri River , their observations on Native nations , and their descriptions of plant and mineral specimens collected among many other details into a manuscript they called the " Mandan Miscellany " , which they sent back to St . Louis with their large keelboat in the spring . Sacagawea . It was apparently also at Fort Mandan that Lewis and Clark first met Sacagawea . Her husband , Toussaint Charbonneau , served as a Hidatsa interpreter for the expedition , and the journals imply that she lived at the fort with him . Her son Jean Baptiste , whom she carried with her throughout the rest of the expedition , was born on February 11 , also possibly at the fort . After 1805 . When the Corps passed back through the area in August , 1806 , on their return journey home , the fort had burnt to the ground ; the reason is unknown . Since that time , the Missouri River has slowly eroded its bank and has shifted to the east , covering up what remained of the charred fort . A replica stands along the river , 2 . 5 miles from the intersection of ND 200A and US 83 . It is located near the North Dakota Lewis and Clark Interpretive Center , which offers tours and interpretive programs about the significance of the Lewis and Clark Expedition in American and regional history . < br >