Eh. The real problem with it is that DR isn't even vaguely relevant by the time you can take it. 7th and 8th level monsters are throwing around 2d8+6 to 2d12+6. -2 damage just isn't worth tracking.
[Barbarians have a similar problem at 9th level, though they can build for slightly higher DR, but it costs a lot of AC or attack bonus, so isn't really worthwhile- realistically they'll end up at DR3, DR4 at 10th]
The attack isn't any good either. It's just a bad feat- stick with the first level ones.
Though I don't know why a mountain would be particularly damaged by fire or force, or even a reasonable amount of acid. The resistance: all makes perfect sense to me.