Rocky Mountains

The Rocky Mountains, often called the Rockies, are the largest mountain system in North America.

This massive range forms the easternmost part of the North American Cordillera. The Cordillera is a large system of mountain ranges stretching along the western side of the continent. The Rockies are distinct from the Cascade Range and the Sierra Nevada. Those ranges lie further to the west and are tectonically younger. The Rockies stretch approximately 3,000 miles in a straight line. They run from Western Canada down to New Mexico in the United States.

The formation of these mountains began between 55 and 80 million years ago. This occurred during a geological event known as the Laramide orogeny. During this time, tectonic plates began sliding underneath the North American plate. In the United States, the Farallon Plate dove under the continent at a very shallow angle. This shallow angle of subduction is unusual. It moved the area of mountain building much further inland than normal. The process caused tremendous thrusts that piled sheets of crust on top of each other. This built the broad and high range we see today. Some researchers suggest a "hit-and-run" model might also explain this uplift. This model involves oblique and transient plate interactions rather than just long-term subduction.

The landscape we see now is the result of millions of years of change. After the Laramide orogeny, the Rockies were a high plateau. They were likely about 6,000 meters above sea level. Over the last 60 million years, erosion has stripped away the high rocks. This erosion revealed much older rocks underneath. These include Precambrian metamorphic rocks that form the core of North America. Some rocks, like the sedimentary argillite, date back 1.7 billion years. During the Paleozoic era, much of western North America was under a shallow sea. This sea deposited many kilometers of limestone and dolomite.

Glaciers also played a major role in shaping the mountains. During the Pleistocene and Holocene epochs, ice ages occurred. These glaciers carved the mountains into dramatic shapes. They created U-shaped valleys and deep basins called cirques.

Recent glacial episodes, like the Pinedale Glaciation, lasted until as recently as 15,000 to 20,000 years ago.

These frozen sheets left lasting marks on the peaks and valleys. Today, the mountains contain a complex mix of volcanic, metamorphic, and sedimentary rocks.

The Rockies are divided into different geographic sections. In Canada, geographers define the Canadian Rockies as areas south of the Liard River. They are split into the Muskwa, Hart, and Continental Ranges. The western edge in Canada is formed by the Rocky Mountain Trench. This huge trench runs the length of British Columbia. In the United States, the range includes many subranges. These include the Teton Range in Wyoming and Idaho, and the San Juan Mountains in Colorado and New Mexico.

The range's width varies from 70 to 300 miles.

A vital feature of the range is the Continental Divide of the Americas. This is a line that determines which ocean water will reach. Water falling on one side flows toward the Atlantic Ocean. Water on the other side flows toward the Pacific Ocean. Some water even flows toward the Arctic Ocean. Triple Divide Peak is a special spot in Glacier National Park. Water falling there can reach the Atlantic, the Pacific, and Hudson Bay. This makes the mountain a unique meeting point for three different drainage systems.

Human history in the Rockies is tied to its resources and beauty. Humans began inhabiting the range at the end of the last ice age. Later, European explorers like Sir Alexander Mackenzie traveled through the area. The Lewis and Clark Expedition also explored these lands. Initially, people came for minerals and fur.

While resources drove early economics, the mountains have never had a very dense population. The average is only four people per square kilometer. However, population grew rapidly in some states between 1950 and 1990. For example, the population of Jackson, Wyoming, increased by 260% between 1972 and 2012. Today, people visit the Rockies for many activities. They enjoy hiking, skiing, and fishing in protected forest lands and parks.