38°49′56″N105°33′16″W / 38.8322°N 105.5544°W /38.8322; -105.5544
TheThirtynine Mile volcanic area, part of the largerCentral Colorado volcanic field, is anextinctvolcanic area located inPark andTeller counties,Colorado, northwest ofCripple Creek and southeast ofSouth Park.[1] The area was the site of significantvolcanism in thePaleogene Period about 35 million years ago.Ashfall andlahars (mudflows) from the volcanoes created the conditions forfossilization at what is nowFlorissant Fossil Beds National Monument.
The Thirtynine Mile volcanic area is the northern reach of an extensiveEocene toOligocenevolcanic belt. The volcanic fields in this belt include, from north to south, the Thirtynine Mile andSan Juan in Colorado, theMogollon-Datil in New Mexico, theBoot Heel in the bootheel of southwestern New Mexico and adjacent areas ofArizona and Mexico, theTrans-Pecos of westTexas, theEastern Chihuahua and the vast volcanic field of theSierra Madre Occidental of western Mexico.[2] These volcanic fields, this volcanic belt, resulted from thesubduction of theFarallon plate under theNorth American Plate.[3][4]
The area is named forThirtynine Mile Mountain, a local peak that is composed of volcanic rocks from the field. The area also contains theGuffey volcanic eruption center.[5]
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