Unusual features of the Laramide orogeny, including a broad area of tectonic quiescence, are found in a broad area from the

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The Laramide orogeny was a period of mountain building that occurred in western North America from about 80 to 40 million years ago. The orogeny was caused by the collision of the Farallon Plate with the North American Plate. The collision caused the Farallon Plate to subduct beneath the North American Plate, which resulted in the formation of the Rocky Mountains.One of the unusual features of the Laramide orogeny is a broad area of tectonic quiescence that is found in a broad area from the Great Valley of California to the Colorado Plateau. This area is known as the "Laramide foreland basin." The foreland basin is a region of subsidence that formed in front of the advancing Rocky Mountains. The subsidence was caused by the weight of the mountains, which caused the crust to flex downward.The Laramide foreland basin is an important feature of the Laramide orogeny because it provides evidence for the timing and magnitude of the orogeny. The subsidence of the foreland basin began about 80 million years ago, which is the same time that the Rocky Mountains began to form. The subsidence continued for about 40 million years, which is the same time that the Rocky Mountains were growing. The amount of subsidence in the foreland basin is also evidence for the magnitude of the orogeny. The subsidence is greatest in the center of the foreland basin, which is where the Rocky Mountains are highest. This suggests that the Rocky Mountains were formed by a very large and powerful orogeny.

Unusual Features of the Laramide Orogeny, Including a Broad Area