Glen,
I remember it well. It was just upgrade from Ah Wilderness guest ranch. My brother, my dad and I hiked up there one day in 1966 when we stayed at the ranch for a few days. I have a B&W around here of 478 departing the tank. We climbed up on the side of mountain just around the curve from the tank, and you could look down on the front and somewhat top of the engine, and got the river in the background. Also on that trip, forest service people had just put up a new wooden sign, that said Tank Creek San Juan National Forest. Lying on the ground a few feet away was the old sign which was broken on one corner. It found its way back to Ohio!!!
Historians can tell you when the tank was changed.
Greg