San Luis Peak

Geology (San Luis Peak)

Title: Volcanism in the LaGarita Range - San Juan Mountains

Entered by: Mark A Steiner

Added: 11/05/2011, Last Updated: 11/05/2011

The geology of the entire LaGarita range, including San Luis Peak, depicts a history of explosive volcanism. When seen from the air, the LaGarita caldera is about 10 miles across. According to the US Geological Survey, vents within the LaGarita Caldera have produced as much as 1,250 cubic miles of volcanic ejecta (ash, cinders and lava flows). This is enough volcanic debris to cover the entire continental United States with about 1-3 feet of volcanic solids. Some of these light-colored ash deposits, called by geologists "tuff" may be found along Tomichi Creek and US 50 between Sargents and Gunnison. The almost moonscape-like terrain in the highest peaks of the LaGaritas frequently alternates between layers of resistant lava beds and incompetent ash beds. Consequently, slumping of volcanic landforms is a common feature in these mountains. High featureless plateaus such as Snow Mesa are expressions of the rim of the caldera.

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