Well done Chris
I followed the tail of the wye and it ended in area that appeared to be surface mined. From that clue a discovery was made of a business by the name of the Chicago Pumice Co. which had mining operations at Black Rock Utah in Milford County as far back as the 1890's. Directly east of the area containing this wye there is a current but undeveloped Pumice claim by the name of the "Stellar Claim".
I do not know enough to claim that this wye and operation had anything to do with the Chicago Pumice Co. for it looks to me like a later operation.
Viewing the area around Black Rock one can see other abandoned railroad grades diverging off the main that also end it what appear to be surface mining operations.

Closer to the ghost of Black Rock this grade can be followed to another surface mining operation.

Just south of Black Rock simply an ancient wye.

A current operation by the Graymont Lime Plant just up the line from the Place Spotting Quiz location can be viewed here.