It’s a fact about North America. If you go far enough east, you will get to mountains. If you go far enough west, you will get to mountains.
But the mountains in the East are different from the ones in the West. The mountains in the East are older. They are lower and more rounded. Trees and other large plants grow to the very top. Mountains in the East are usually not cold enough to have snow all year. Yet all mountains in North America are full of life.