Who were the Europeans who had ventured west of the Mississippi before its exploration?

The so-called "mountain men" traveled hundreds or thousands of miles beyond charted territory to find furs.They made the first European contact with many Native American tribes and often formed friendships and business partnerships with them. Native American people even taught these mountain men some of the skills they needed to survive in their new environment. When mountain men returned from their journeys they told stories of the wild, rugged lands that they had encountered. Yet, by 1800, the majority of European Americans still had no idea what existed beyond the Mississippi.

Answer: fur traders