Why are the Rocky Mountains called rockies for short?

The Rocky Mountains are not called "Rockies" for short. They are called the Rockies because they are rocky. The name "Rocky Mountains" was first used by the French explorer Pierre Gaultier de Varennes, sieur de La Vérendrye, in 1743. He named them after the many large rocks and boulders that he saw in the mountains. The name "Rockies" is a shortened form of "Rocky Mountains".