The round "Scenic Line" "Toilet Seat" herald (I'll draw fire for that one!
) came in two basic versions: One with Royal Gorge Route in the middle and the other with Moffat Tunnel on top then Royal Gorge underneath. This latter would have come in 1935 with the completion of the Dotsero Cutoff from Dotsero to Orestod opening the direct line to the Front Range through the Moffat Tunnel. So Royal Gorge Route from the late 20's to 1935 then a mixture of the two after that until they were replaced by the speed script, or flying, Rio Grande beginning in 1940.
I don't have my materials here with me at work to verify the dates but I think those are pretty close. Good ballpark estimate, anyway!