I'm not an expert on such things, but I do know that computers everywhere had to download an update to get hip to the new DST rules. Presumably your clock does not have a way to download new DST rules.

You can set it to mountain time, for sure, although I'd make a guess that this time next year, it'll be off by another hour, so you'll have to set it to Pacific. After about 5 more years, you'll run out of time zones.