To add to the info above.
I would HIGHLY recommend looking at maps before you go. The GNWR is a very tough RR to railfan, since most of it is beyond the reach of highways. There is a road from Lewiston that follows the tracks and river almost to Lower Granite dam. There is a road to Lower Granite dam. There is a road that crosses the river/tracks at Central Ferry (WA 127), there is gravel road to Little Goose Dam, and there is a road that crosses the river/tracks at Lyons Ferry (WA 261). Other than that, you are pretty much out of luck as far as actually getting close enough to get good shots, unless you have a boat and want to follow it on the river. Because of how fast they run, you can get them at one location, but won’t have time to drive miles out of the way to get to another location. The GNWR is pretty much a one shot railroad, meaning that you have to pick a location and wait for the train to come to you to get one shot and then you are done for the day.
From Lewiston they run 40 MPH (last I heard anyways) so you can get them coming out of the yard, but because of having to go through town, won’t be able to catch them after they cross the river. I would suggest that if you plan to start in Lewiston, set up on the north side of the Clearwater River Bridge (the big drawbridge in Lewiston) and then take Wawawai Rd towards Lower Granite. Or, pick one of the other locations that you can get to on the Snake River and get a few shots there. Good luck, I hope you are able to get some good shots since this is a rarely seen railroad because it is a difficult one to see.
Matt F
Moscow ID