We discuss all the reasons why people were moving (to explore, to have more land, to find gold, etc). Then we map out the different trails explorers took.
To do this I blow up a map of the United States. I give each student a clump of clay. The clay is used to make mountains. They do this part first. Then they use their books and their markers to draw out the paths taken. Have them use a different color for each trail and add it to their legend. Most of the time you will hear complaints about it being hard to draw the trail because the mountain is in the way.
This is when I tell them how hard it must have been to get around the mountains on their wagons.
This project is a lot of fun because it teaches states, direction, landforms, and helps them understand how hard the trip must have been.