At this point, the expedition encountered a fork in the river and faced a critical decision. Which branch was the Missouri and which was a tributary? Both streams were roughly equal in size. One headed off in a northerly direction. The other angled south. Exploration parties were sent up both streams and, after several days of scouting, Lewis finally determined correctly that the Missouri was the less silt-laden, southerly stream. He named the tributary after his cousin Maria Wood.