Do some species of Juniper trees only grow at certain elevations?

I live in Pocatello, Idaho. Pocatello is located in a valley and we're surrounded by mountains. Pocatello sits at about 4,500 feet elevation. As I was studying a mountain in east Pocatello, Chinks Peak, (sorry that's what we call it) I realized that it's foot hills are covered in junipers, but you can almost see like a tree line where they stop growing. Here's a few pictures: http://flickr.com/photos/phydeaux460/562717135/

http://flickr.com/photos/14914579@N00/2175968452/

http://flickr.com/photos/phydeaux460/333483012/

The side of Chinks that faces Pocatello is very dry. The other side is densely covered in timber- not near the same amount of junipers.

The Mink Creek area is south of Pocatello. It's home to Pocatello's biggest mountain- Scout Mountain. It's foothills are also covered in junipers, but they're virtually nonexistent on Scout Mountain. The Mink Creek Area is anywhere between 5,000 to 8,600 feet.

http://flickr.com/photos/homemadeoriginals/7157750...

Anyone know if my suspicions are correct?