The Front Range of the Rockies

The geological history of the front range of the Rocky Mountains is just as jumbled and complicated as the mountains appear from this vantage point. Geologic forces far to the west caused this remarkable backdrop. About seventy million years ago, the subduction of the Farallon tectonic plate under the North American plate gave rise to the Rockies. Over millions of years, the crust pushed upward and then slid the older rock west over the top of the younger rock. Called an overthrust fault, it pushed up, deformed, and folded the rocks as it moved. Pleistocene ice sheets later carved the rocks into the scrambled geological appearance we see today. The gray rocks are Madison limestone. About 350 million years ago, much of Montana was submerged under a shallow sea. Billions of tiny marine creatures thrived in the water and when they died their bodies settled into the muck on the seabed. After hundreds of millions of years of accumulation and many more millions of years it metamorphosed into the pale gray rocks of the front range. Because Madison Limestone resists weathering and erosion much better than most other kinds of rocks, it created the spectacular cliffs and dramatic ridges you see west of here. The front range has been a paradise for wildlife for at least seventy million years. Duck-billed hadrosaurs and triceratops once roamed the shores of an ancient sea. Now is the home of many different species, including Grizzlies, elk, mountain lions, deer, wolves, moose, and rattlesnakes.