Is this perhaps the frost-box of one of the Garos tanks (or foundation of the pumphouse):
It appears highway 9 clobbered anything that may have remained of the section house foundations, but the wye for the Alma branch can still be seen directly behind the Garos general store:
Speaking of which, ~1900 from the Park County Archives:
... and, remarkably, as of 2012:
Further South there appears to be another wye with a forked tail:
A bit further south again is another water tank foundation (and if you pan this map yet again south, you'll find a third wye). Based on Mac Poor's map, I believe these last two are "Platte River".
Mac Poor has the salt works even farther south, so that doesn't fit with the middle (forked tail) wye. Anyone know what it is?
Cheers,
Jeff.