Sod houses were the homes that homesteaders made when they moved West. Since there were no trees, or lack of trees homesteaders had to make their homes of the clay like ground where they settled.
Sod houses were not the ideal homes. They were dirty, snakes and rodents would live in the walls. The ceiling was covered by a tarp to keep the dirt from falling down while you slept. But the sod house worked for what the homesteaders needed, a roof over their head to sleep under.
After more people had settled, they started growing trees, which then they would build log houses, instead of sod houses. After trees became more localized, sod houses became log houses