Interesting topic. I found a 1951 Texas plate in the road ditch South East of Baker, MT about ten years ago it was yellow in color and a shorter plate that those pictured. That was about the time oil was discovered in this area.
BMR,
I know that the tax structures are different between MT an ND but I heard on another blog that although there are leases in Sheridan,Roosevelt and Richland Counties in MT the companies still have to drill in ND to hold there leases over there. I expect there are only so many rigs to go around.