I spent the summer of 1982 working at Canyon Lodge in Yellowstone. It's a cold place. It snowed on the 4th of July that year. I don't even think most of the facilities were open until early June or late May because it might take until then to get the road through the passes cleared. They closed the place for the winter after Labor day.

That there is climbable ice on the south (mostly sun free) side of a deep canyon -- even in June -- would not surprise me.