They follow a wagon trail west into the part of Kansas that was called "Indian territory" at the time. Mr. Ingalls knows that the land belongs to the American Indians but he thinks the United States federal government is going to change its mind about that. He thinks they will say that white people can settle in Kansas soon. He wants to build a farm before all the good places are taken. He sees a good place near a valley with a river in it, stops the wagon, and starts building a house out of logs from trees from the valley.