The largest mountain chain in North America is the vast, complex system known as the North American Cordillera. This system is not a single, continuous range but comprises a diverse arrangement of mountain ranges, intermontane plateaus, and basins. The Cordillera is an integral part of the American Cordillera, which extends almost continuously along the Pacific coast from Alaska to the southern tip of South America. It is the most significant geological feature of western North America, defining the region’s physical geography and climatic patterns.
The North American Cordillera: Scope and Scale
The North American Cordillera is the largest and most extensive mountain system on the continent, stretching approximately 4,000 miles (6,400 kilometers) from the Brooks Range in Alaska down to the southern border of Mexico. This massive geological formation spans a considerable portion of three countries: Canada, the United States, and Mexico. Its immense geographical reach is a primary reason it is considered the largest mountain chain, encompassing nearly all of the mountainous terrain west of the Great Plains.
The system reaches about 1,000 miles (1,600 kilometers) wide at its midsection between California and Colorado. This width consists of a succession of parallel ranges separated by lower-elevation plateaus and basins. The Cordillera also hosts the Continental Divide of the Americas, a hydrological boundary separating watersheds that flow to the Pacific Ocean from those draining into the Atlantic and Arctic Oceans.
Distinct Segments of the Cordillera System
The Cordillera is structurally organized into several distinct, roughly parallel mountain belts that reflect different geological histories. The easternmost of these is the Laramide Belt, which includes the well-known Rocky Mountains in the United States and Canada, and the Sierra Madre Oriental in Mexico. These ranges are characterized by high, rugged peaks and were formed by significant inland uplift and crustal shortening. The Rocky Mountains themselves stretch over 3,000 miles from New Mexico to British Columbia.
Moving westward is the Interior Belt, which contains the Sierra Nevada in California and the Cascade Range of the Pacific Northwest. The Sierra Nevada is known for its massive granite batholiths and towering peaks like Mount Whitney. The Cascade Range is defined by its chain of prominent, active and dormant stratovolcanoes, such as Mount Rainier. These interior ranges represent the core of the ancient magmatic arc system that developed during the Cordillera’s formation.
The westernmost segment is the Pacific Coast Belt, which directly borders the Pacific Ocean. It includes the Coast Ranges of California, Oregon, and Washington, and the Coast Mountains of British Columbia and Alaska. This belt is a complex mix of accreted terranes and active fault systems, featuring dramatic fjords and dense temperate rainforests.
Geological Origins and Development
The formation of the North American Cordillera is a prolonged and complex process rooted in plate tectonics, beginning in the Mesozoic Era. The primary driving force was the subduction of various oceanic plates, most notably the Farallon Plate, beneath the westward-moving North American Plate. This convergence along the continental margin caused intense compression and deformation, which uplifted and folded the crust.
Mountain building occurred in several major phases, known as orogenies, over tens of millions of years. The Nevadan orogeny, occurring in the mid-Mesozoic around 155 to 145 million years ago, was linked to the intrusion of large masses of magma that cooled to form the deep granitic cores of ranges like the Sierra Nevada.
The Sevier orogeny, spanning from approximately 160 to 50 million years ago, followed the Nevadan phase. This event created a large fold and thrust belt in the eastern Cordillera through low-angle faulting.
The final major phase was the Laramide orogeny, occurring from about 80 to 35 million years ago. This phase is responsible for the uplift of the Rocky Mountains farther inland than most subduction-related mountain chains. This inland uplift resulted from “flat-slab” subduction, where the angle of the subducting oceanic plate became unusually shallow, pushing the deformation far into the continent’s interior.