Diesel locomotive No. 1685 was built by General Motors Diesel (GMD) in March 1957 for the Midland Railway Company of Manitoba. It was absorbed by BNSF and was donated to the Society by BNSF in July 2010.

No. 1685 is used on the Prairie Dog Central in regular service and in some charter service. It acts as backup power should No. 3 or 4138 be unavailable.