The Alps.
Pioneers needed to cross the Appalachian mountain range in order to get to Kentucky and Tennessee. They used the Cumberland Gap, a path through the mountain range, to do so.
Sierra Nevada
You cross the Andes.
Caucasus mountain range.
On foot, horses and elephants.
Cascades
The Alps.
The Ural mountain range separates Europe from Asia. This range is difficult to cross and has been a natural barrier for centuries.
I think it is MOSSIF as i have done a cross word where the part of a mountain range is MOSS_F so perhaps that is it? x
Rocky Mountains
Your moms breast! :D
They crossed the Rocky Mountain Range...good luck!