Drew,
Inasmuch as I don't know the specifics of the Black Butte to Ashland topology down to nuts and bolts, that section was the main line before the bypass through Klammath Falls was built. I don't believe that the grades are any steeper than the Tehachipi or Donner route, even at peak intermittent gradient of better than 3.0%. According to Dan Ranger's article in Trains magazine (Aug 1968), the only boiler explosion of a cab forward was at Cooper, CA just north of Salinas, which was tangent track. I do remember a story of an AC coming apart at the frame somewhere south of Ashland. When any locomotive is on tangent track, the crown sheet should be horizontal. What about the internal boiler design of an AC would it make more susceptible to uncovering the crown sheet more than any other locomotive at a specific angle of tilt? I think there is valid concern over the gradient with a poorly maintained or malfunctioning locomotive. Steep gradient is a problem with crown sheet coverage in any steam locomotive. If there was an initially recognized problem from gradient with the ACs, it seems they would never have been allowed to operate there in the first place. I suggested that section of line because of low business levels and the danger of abandonment if someone doesn't put it to greater use. Of course the ideal place would be Bay area to Reno, but if UP is kicking up a fuss about not wanting passenger operations from a Capitol Corridor extended to Reno, then forget about steam for now. What impact a re-double-tracking of the Hill would make eventually could only be speculated. That is why I made the comment that anyone who proposes to operate steam on UP/BNSF main lines had better be able to demonstrate a very abnormally high reliability aspect to their proposed locomotive before even having a snowball's chance in Thermal of being considered.