Is the Yellowstone 2-8-8-4 locomotive not named for the national park.
Indirectly yes. NP developed the first 2-8-8-4 class to handle the low quality Rosebud coal. The loco had to have a huge firebox to do that. Hence the 4 wheel rear truck. Since the NP was serving Yellowstone National Park and using it big time for marketing purposes they choose that name for the loco.
There are lots of web sites with this info. Search for Yellowstone Locomotive.
The NP Z-5 class 2-8-8-4s were designed to solve an operating problem between Glendive Montana and Mandan North Dakota. East of Mandan a W-3 or W-5 Mikado could handle a 4000 ton train on its own. Further west slow but powerful low drivered Z-2, Z-3 and Z-4 class 2-8-8-2 Mallet compound locomotives were used as helpers on long mountain grades. But between Glendive and Mandan there were many short sections of 1% grades that confronted both eastbound and westbound trains. The multiple sections of 1% were too short and too numerous to each be its own helper district so 4000 ton freights were either double headed by Mikados or broken into two 2000 ton trains. The 2-8-8-4 simple articulated wheel arrangement with 63 inch drivers was selected to allow one locomotive to do the work of two Mikados and make Mikado like speed. The Z-5 did just that for the NP and were the preferred power for this tough section of the NP for about 15 years until FT diesel-electrics came on the scene in the 1944.
When built the NP Z-5s were the largest locomotives in the world and held that title until the arrival of the UP Big Boy. They had the largest firebox ever installed on any locomotive. In fact, the fire box with its 182 square foot grate area was so large that it was not only supported by the 4 wheel trailing truck but the last two driving axles as well.
The Northern Pacific put great efforts into promoting Yellowstone National Park and I am sure they were happy to have the worlds largest locomotives help draw attention to it. However, it was not coincidental that the line between Glendive and Mandan for which the Z-5s were designed was part of the Northern Pacific's Yellowstone Division which also paralleled the Yellowstone River for many miles.