Tales of Topographic Maps
IDK the exact time-frame, but in the time around the end of the Chase, Forrest's collection of topographic maps were being offered to the public. Do we know how or to whom those maps were disposed?
Digging a bit deeper into that area stretching from the Caldera Rim Picnic Rest Spot, then through the Gibbons Falls (aka Wylie's Lunch and Permanent Campground) and past Madison Junction, then out to West Yellowstone an interesting idea emerges.
It appears that because the Yellowstone Erupted at least three times, there are several Caldera Rims: from a non-professional viewpoint I think that there are some were places where the rims overlapped and intersected with one another.
Is it possible that the Secret Creek Valley is actually what formed from the space between the BORDERS of two Caldera Rims? On GE it looks like the top of this valley ends near Purple Mountain, overlooking Madison Junction.