Geology

Tremendous Forces Shaped the Land

The cliffs and boulders along the Frontier Pathways Scenic and Historic Byway tell of ancient oceans, volcanoes and sandy beaches. You can see the oldest rocks along the byway in Hardscrabble Canyon, west of Wetmore. There, the granite and banded gneiss (pronounced nice ) are over a billion years old! During its formation, the granite was once so hot, it was molten, and then it slowly cooled into solid rock.

Over the ages, forces of wind and water deposited sediments over the land. About 130 million years ago in Colorado, a sandy beach lay along the edge of an Inland Sea. Dinosaurs roamed over the warm sands. Over time, the sand grains hardened into tan Dakota Sandstone.

The Inland Sea slowly advanced covering the beach sands. First, muds were deposited that would later form black Graneros shale. Next, shells of sea creatures helped form blocky Greenhorn limestone. Then, as the sea was almost filled with sediments, the gray Carlile shale was deposited. Finally, a beach environment returned, leaving tan Codell sandstone.

Around 100 million years ago, the Inland Sea returned. Strange creatures swam in this ancient ocean. Primitive reptiles, such as 20-foot-long mosasaurs, hunted for fish in the warm water. Ammonites, relatives to the chambered nautilus, were up to six feet across. As these and other shellfish died, their shells helped to form the gray Fort Hays Limestone.

Tremendous mountain-building forces lifted the granite, gneiss and sedimen tary rocks about 65 million years ago. The upthrust formed the Sangre de Cristo Mountains and the Wet Mountains. More uplift occurred starting around 37
million years ago. During this period, the molten rock brought precious metals to the surface near the present day towns of Rosita and Silver Cliff.

The mountains didn’t receive their rugged shape until the last two million years. During the Ice Age, alpine glaciers gouged bowl-shaped valleys, calcirques, into the Sangre de Cristos. Today, wind, water and ice continue shape the mountains and the landscape.