Santa Fe's first northern, No. 3751 was also the first northern delivered by the Baldwin Locomotive Works. This class of engine was built in 1927 as an enlarged version of the earlier 3700 class 4-8-2 Mountain type locomotives. They 3751's shared a striking resemblance to the 3700s as built, which earned them the nickname "Heavy Mountains". They served reliably with the AT&SF until the late 50s, when they were all retired. 3751 was later restored, and still remains in operation as the oldest operating 4-8-4 in the US.

The version of the locomotive depicted here is how she looked as delivered from Baldwin. The rebuilt version of the locomotive will be made at a later date.