On January 1, 1956, the last full year of SP std. gauge steam, the railroad had 12 different types of wheel arrangements still active. They were:
0-6-0, 2-6-0, 4-6-0, 4-6-2
0-8-0, 2-8-0, 2-8-2, 4-8-2, 4-8-4
2-10-2
2-8-8-4 (3804 and 3805 on the Modoc)
4-8-8-2
Why was such an archaic design like the low powered, Stevenson timed Mogul still on the roster?
Answer that was given to me by several steam era rails was that they were liked for their long legged 63" drivers.
They could keep out of the way of fast freights and passengers while on the main line.