In the steam days, it seemed like helpers were often cut off at the summits of grades. For Mullan that would of course be Blossburg. I figured there must be a wye at Blossburg for turning the old steam helper, and yep, sure enough I see a wye there on Google maps.
Pdx:
Did you ever explore this old grade over Mullan Pass? Pic of a collapsed wood trestle:
[www.railpictures.net]