There are also some unique A1A-A1A engines that BNSF has, using 6 axles to spread the weight over the rails, and during instances where all of the weight being on powered axles is desired, the center axles are lifted out of the way, placing all of the weight on motored axles.
The end result: a locomotive that combines the best qualities of a 4 axle (all axles powered) with a 6 axle loco (better weight distribution).
Most of the "Heritage" engines that we saw on vacation were of the Santa Fe variety. The WarBonnet is a striking paint scheme, at least except for the BNSF SD70MAC #9647, the "WarVomit".