The Precambrian rock (Appekunny Formation - 1.3 billion years old and Altyn limestone - 1.45 billion years old) that makes up Chief Mountain is the remnant of rock that was thrust over younger Cretaceous rock below.  Look for ripple marks, raindrop prints, and mud cracks along with fossils of algae in the Precambiran rocks.  The placement of older rocks on top of younger rocks occurred along a large thrust fault as part of the formation of the Rocky Mountains (the thrust occurred between 170 and 70 million years ago).