Well, it's not that bad, but it would have required some engineering skills akin to those needed for the CP over Donner Pass or the D&RG through Royal Gorge.

It is somewhat suprising that UP never considered bypassing Hell's Canyon to the east, utilizing the Weiser branch to New Meadows, then building the connector line down the Little Salmon and Salmon River canyons to Lewiston. Granted, there would be an uphill climb from Weiser to New Meadows, but having driven along that route via US 95 it seems the northbound nee-westbound grade is fairly easy. I expect the worst gradient would have been that short 8 miles between the old Pine Ridge mill site and New Meadows over the Weiser/Salmon divide. Does anyone have a profile map of that line that they could share?

Since US 95 runs along this route all the way to White Bird it is logical a rail line would be a relative cinch to build. The only real rugged part would be the short section near the confluence of the Salmon and Snake rivers.

Again, hindsight is 20/20 - if the UP had gone ahead and built that line, it'd be paying huge dividends right now!