If you don't already have it, an excellent book is Steam Along the Boundary, by Robert D. Turner and J.S. David Wilkie. It gives the history of southern BC railways. You can access the former lines in many places: Greenwood, Castlegar, Cranbrook, Christina Lake (I have cycled the line above Christina Lake, from Paulson to Christina Lake and down across the steel trestle across the Kettle River - Columbia and Western Rail Trail. It helped that there were two of us, each with a vehicle, so we drove up to Paulson with our bikes, leaving the other vehicle at Christina Lake).