 In May <unk> , the French explorers Louis Jolliet and Jacques Marquette left the settlement of St. Ignace on Lake Huron and traveled down the Wisconsin and Mississippi Rivers , aiming to reach the Pacific Ocean . In late June , Jolliet and Marquette became the first documented European <unk> of the Missouri River , which according to their journals was in full flood . " I never saw anything more terrific , " Jolliet wrote , " a tangle of entire trees from the mouth of the <unk> [ Missouri ] with such <unk> that one could not attempt to cross it without great danger . The <unk> was such that the water was made muddy by it and could not clear itself . " They recorded <unk> or <unk> as the local name for the Missouri . However , the party never explored the Missouri beyond its mouth , nor did they linger in the area . In addition , they later learned that the Mississippi drained into the Gulf of Mexico and not the Pacific as they had originally presumed ; the expedition turned back about 440 miles ( 710 km ) short of the Gulf at the confluence of the Arkansas River with the Mississippi . 
