Everett M. Greene wrote:

Having no experience with or data about the Helena IFR procedures,
but having experience with the high Sierras and Rockies, I would find
it hard to believe the someone would "hit some granite" without being
way out of bounds. I'd describe the terrain around Helena as gently
rolling, not mountainous. Even the mountains to the west are little
more than big hills.

The article I recall was in the pre-GPS days and the pilot became
disoriented/distracted by ice in addition to inability to lose
altitude sufficiently quickly, so it's possible that he was out of
bounds. (It's also possible that this occurred at a different airport
altogether or not at all -- the article was written and read by me
many years ago.)