Thirtynine Mile volcanic area
The Thirtynine Mile volcanic area, part of the larger Central Colorado volcanic field, is an extinct volcanic area located in Park and Teller counties, Colorado, northwest of Cripple Creek and southeast of South Park. The area was the site of significant volcanism in the Paleogene Period about 35 million years ago. Ashfall and lahars (mudflows) from the volcanoes created the conditions for fossilization at what is now Florissant Fossil Beds National Monument.
- McIntosh, William C.; Chapin, Charles E. (2004). Geochronology of the central Colorado volcanic field (PDF). New Mexico Bureau of Geology and Mineral Resources, Bulletin 160. Retrieved 2010-03-31.
- Wobus, Reinhard A.; et al. (July 1990). "Geochemistry of high-potassium rocks from the mid-Tertiary Guffey volcanic center, Thirtynine Mile volcanic field, central Colorado". Geology. 17: 642–645. Retrieved 2016-03-21.
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