What kind of shack?

 

This old shack seems an unusual structure for the region. It doesn't look like a homesteaders house (though many of them were quite modest), nor does it look like a typical outbuilding.
The yellow paint, the round hole on the front, which would have contained a steel plate to insulate the building from the stovepipe, both say railroad to me.
I'm tempted to believe it may have been left over from the old Chicago, Rock Island & Pacific Railroad, which was very close by. It may have been a "section shack," (also known as a section house), a small building where track maintenance workers kept their tools, lunches, and the such, now repurposed for ranch use, much like the old freight cars that dot the area.
It sits just east of Tucumcari, a road or two down from Route 66, not far from Old House 137.