intermountain

As a noun terms

is .

As an adjective intermountain is

between mountains.

As a noun mountain

is a large mass of earth and rock, rising above the common level of the earth or adjacent land, usually given by geographers as above 1000 feet in height (or 3048 metres), though such masses may still be described as hills in comparison with larger mountains.

As an adjective intermountain is

between mountains.