Thank you. I read my report on KCFW TV from Kalispell, and they didn't mention a cause. The Missoulian wants me to pay for the news, and they don't have enough of interest to me on a regular basis to be worth it, so I quit reading them several years ago.
Was it at a switch, and the cars "cornered" or sideswiped, or was the scrap metal car on the same track? A hard coupling by a runaway car seems unlikely to have turned the tank cars over, but stranger things have happened.