Don't mean to cut in on William as he's worked there a lot more recently than I did.
Railroad is 64 miles give or take from WMS to the Canyon. Profile is a shallow vee with the low point being at Mile 36 near Willaha. From around Mile 12 to the west end of Miller Wash, about 20 miles, it still should be 40 mile an hour track. After the speed restriction at Miller Wash, it's 40 again to just after Anita, then down to 30 for the 3% climb to Imbleu. Mostly 25 from there to the Canyon. Forested at each end where it's a little higher elevation and quite open in the middle. Still a fine ride and best way to get there.