Evolved
In Red, my Kangaskan evolved a M', I forget but I remember I was in a mountainous region when it happened and there was a cave enterance. That might give you some clues to its levels depending on the leve of the wild pokemon in regions with grass near a cave enterence. If I had to say it was around level 30 or so. At any rate I was shocked, I had a gameshark but it wasn't in at the time and I had done the item duplication trick a few times (I don't think I caught missingno tho).