valleys
Its a hill
A low hill at the base of a mountain is typically called a foothill. It serves as a transition between the flatlands and the more rugged terrain of the mountain. Foothills are often characterized by gentle slopes and can be rich in vegetation.
Valley
valley
A foothill.
The low lands between hills or mountains is called a valley.
A synonym for mountain could possibly be a hill.
valley's
A bridge.
How high it is. Too low, and it's considered a hill instead.
There is no universally agreed definition of mountain; in the UK anything over 600m is considered a mountain, but in the USA some landscapes as low as 30m are called "mountains", also in the Gambia there is a "mountain" of 53m height. The short answer, with such an arbitary difference between hill and mountain, its impossible to say.
Valleys are low-lying areas between hills and mountain ranges, often formed by erosion from water or glaciers. They are characterized by fertile soil due to the deposition of sediments and usually have a river or stream running through them. Valleys provide habitats for diverse flora and fauna and are important for agriculture and settlement.