Rio Grande/D&S change-over

While cleaning out media files I came across a nice scene on the highline in the morning. Its 476 and the lettering is still Rio Grande. I originally thought I shot this in 1981, on the honeymoon trip, but didn't remember walking in that direction from Rockwood, although the wife and I did hike from AH! Wilderness to the High Bridge and back one day while staying up there. So, I thought the Bradshaw purchase happened sometime before the 81 season(When we were there), and thus I thought the lettering should have been D&S. So either they still used Rio Grande lettering in late June 1981, or I shot this at some unknown time before that. It has sound on the film so it has to be after 1978, but I don't remember doing any trips between 1976 and 1981!!!! Any ideas!
Greg