My maternal grandmother was born in a sod house in Montana when her parents were homesteading there at the turn of the 20th century. They lived there until she was five and were able to sell their claim and returned to be nearer family in Nebraska. The sod house she described was much more of a lean-to, built into a hillside.
Here's another shot clearly showing the Maytag N2. Regarding this house, apparently they clad the exterior with boards, leaving the original sod walls inside. Must be excellent insulation!