By Vince Matthews
Colorado has seen its share of volcanoes. Numerous volcanoes erupted here during several geologic periods. This fiery activity spanned the gamut of volcanic types. Three major eras of eruption were 1.75 to 1.72 billion years ago, 38 to 26 million years ago, and 26 million years ago until the present. The most recent eruption in Colorado was a mere 4,135 years ago, where I-70 crosses the basalt flow between Gypsum and Glenwood Canyon.
About 27 million years ago, it is estimated that two thirds of Colorado was covered by volcanic strata. The Upper Arkansas and San Luis Valleys were in the midst of much of this red-hot activity and are home to volcanic rocks of many different types and ages. We have cinder cones, shield volcanoes, strata-volcanoes, subaqueous pillow lavas and rhyolite lava domes, as well as world-class calderas.