"Mountain minor" is a very elastic term. Often it is used to refer to a particular banjo tuning (gDGCD, or aEADE if capoed up 2 frets). The other common term for this tuning is "Sawmill". In this sense it is not really a scale with a distinctive set of intervals, rather it is a tuning that lends itself to playing in minor keys. And of course, old time banjo was very influenced by modes that were still in use in traditional music.