the mother mesa bears seem to be the PH for Ursalua the named bear for armor quest. The can spawn outside the cave or inside and normally after they are killed Ursalua will spawn nearby.
Always has "a mesa bear cub" following it... doesn't always attack the same thing the mother is though, so sicking a pet at it while soloing will usually keep it busy...
Had the mother drop Bear Heart, Low Quality Bear Skin and Shiny Bear Tooth... while I can't say for sure, it probably shares a loot table with the normal mesa bears...