The rail installed by SVRy on their mainline in 1937 was relay rail leased from UP. It was a variety of sizes from 70lb up to 90lb on the dual gauge. SVRy then used the removed 45lb steel rail to relay their sidings, spur, wyes and yard track which had contained a lot of the original 56lb wrought iron rail that likely came from U&N in the earliest days. I don't know what they did on the Middle Fork except I understand, from what source I am uncertain, that is was rebuilt as well. The SVRy mainline upgrade included treated ties processed at the rr's own plant in S.Baker along with new crushed ballast produced by the rr's own crusher. I think the pit was located not far above the present Mason Dam on the W.side. As I recall the track and siding maps show a spur built into this pit. OLC had some of the former Utah Construction Co. ballast cars just like SVRy's which were purchased around time of the rebuilds, so this fits in. There is a section of rail I looked at some years ago right along the middle fork road that was not real light stuff, but I don't recall what. Using the former SVRy 45 rail would have made economic sense unless most of the 45lb was so worn out that it was not worth relaying.