Untitled Sighting

In 1985, I was attending Indiana State University in Terre Haute, IN.  One Saturday morning I was travelling to Chicago to visit relatives. I was driving north on U.S. 41 and I looked to my right down into a small valley (more a depression in the land than a valley) with a small stream running through it. About 100-150 yards from the highway, I saw a large dark-colored creature walking away from the road (to the east.) It was very broad and I could clearly see the creature's arms swinging. My view of the bottom part of it was obscured by tall grass and I could only see the very tops of its legs. The head never turned at all. I saw this for 4-5 seconds before the trees on the north side of the depression obscured my view. There were also trees on the south side. My immediate thought was that I didn't really see what I thought I did. I continued driving, unsure of what to do. After a few minutes, I turned around and drove back past where I had seen it (my view from this side of the highway was blocked), turned around again, drove to the bridge where the sighting occurred and stopped where I had originally seen it. There was nothing there at this time. Not being aware of any sasquatch sightings in this area (or the Midwest in general), and not knowing what else to do, I continued on to Chicago and didn't think much more about it for many years.