Intro Igneous rock is formed from magma that has cooled and become solid. Molten rock is extraordinarily hot, sometimes exceeding 2,000 degrees Fahrenheit. If this molten and partially crystallized material (magma) solidifies underground before it reaches the surface, the rock is intrusive or plutonic. If magma travels up through Earth’s crust and reaches the surface, the resulting rocks are extrusive or volcanic. Magma that reaches the surface forms a variety of volcanic landforms and deposits. Today, resistant volcanic flows cap mesas such as Grand Mesa, White River Plateau, Raton Mesa, and those near Basalt, Colorado. In the southwestern part of the state, ash-flow tuffs cover thousands of square miles. The tuff is created from the ash that is blown from the volcano to blanket the landscape. An ash-flow eruption creates a roughly circular depression called a caldera. There are at least nineteen calderas in Colorado, making the state one of the world’s best outdoor laboratories in which to study their formation.
Publications General geological interest Many of these are out of print but may be found on Amazon or other online sources. Chronic, Halka. Roadside Geology of Colorado. Miscellaneous Investigations. Missoula, MT: Mountain Press Publishing Company, 1980. Foutz, Dell R. Geology of Colorado Illustrated. Grand Junction, CO: Dell R. Foutz, 1994. Hopkins, Ralph Lee, and Lindy Birkel Hopkins. Hiking Colorado’s Geology. 1st ed. Seattle, WA: Mountaineers, 2000. Johnson, Kirk R, Robert G. H Raynolds, Jan Vriesen, Donna Braginetz, Gary Staab, and Denver Museum of Nature and Science. Ancient Denvers: Scenes from the Past 300 Million Years of the Colorado Front Range. Denver, CO: Denver Museum of Nature & Science, 2003. Johnson, Kirk R., and Richard Keith Stucky. Prehistoric Journey: A History of Life on Earth. Golden, CO: Fulcrum Publishing, 2006. Matthews, Vincent and Colorado Geological Survey. “SP-57 Tourist Guide to Colorado Geology.” Special Publication. Denver, CO: Colorado Geological Survey, Department of Natural Resources, 2009. Matthews, Vincent, Katie KellerLynn, and Betty Fox, eds. SP-52 Messages in Stone: Colorado’s Colorful Geology. Second. Special Publications, SP-52. Denver, CO: Colorado Geological Survey, Department of Natural Resources, 2009. Murphy, Jack A. Geology Tour of Denver’s Buildings and Monuments. Historic Denver Guides. Denver, CO: Historic Denver and the Denver Museum of Natural History, 1995. Murphy, Jack A. Geology Tour of Denver’s Capitol Hill Stone Buildings. Miscellaneous 65. Denver, CO: Historic Denver, Inc, 1997. Osterwald, Doris B. Rocky Mountain Splendor: A Mile by Mile Guide for Rocky Mountain National Park. 1st ed. Lakewood, CO: Western Guideways, 1989. Raup, Omer B. Geology along Trail Ridge Road: Rocky Mountain National Park Colorado. Estes Park, CO: Rocky Mountain Nature Association, 2005. Reed, Jack, and Gene Ellis. Rocks Above the Clouds: A Hiker’s and Climber’s Guide to Colorado Mountain Geology. The Colorado Mountain Club, n.d. Taylor, Andrew M. Guide to the Geology of Colorado. Golden, CO: Cataract Lode Mining Co., 1999.
General geological interest Many of these are out of print but may be found on Amazon or other online sources. Chronic, Halka. Roadside Geology of Colorado. Miscellaneous Investigations. Missoula, MT: Mountain Press Publishing Company, 1980. Foutz, Dell R. Geology of Colorado Illustrated. Grand Junction, CO: Dell R. Foutz, 1994. Hopkins, Ralph Lee, and Lindy Birkel Hopkins. Hiking Colorado’s Geology. 1st ed. Seattle, WA: Mountaineers, 2000. Johnson, Kirk R, Robert G. H Raynolds, Jan Vriesen, Donna Braginetz, Gary Staab, and Denver Museum of Nature and Science. Ancient Denvers: Scenes from the Past 300 Million Years of the Colorado Front Range. Denver, CO: Denver Museum of Nature & Science, 2003. Johnson, Kirk R., and Richard Keith Stucky. Prehistoric Journey: A History of Life on Earth. Golden, CO: Fulcrum Publishing, 2006. Matthews, Vincent and Colorado Geological Survey. “SP-57 Tourist Guide to Colorado Geology.” Special Publication. Denver, CO: Colorado Geological Survey, Department of Natural Resources, 2009. Matthews, Vincent, Katie KellerLynn, and Betty Fox, eds. SP-52 Messages in Stone: Colorado’s Colorful Geology. Second. Special Publications, SP-52. Denver, CO: Colorado Geological Survey, Department of Natural Resources, 2009. Murphy, Jack A. Geology Tour of Denver’s Buildings and Monuments. Historic Denver Guides. Denver, CO: Historic Denver and the Denver Museum of Natural History, 1995. Murphy, Jack A. Geology Tour of Denver’s Capitol Hill Stone Buildings. Miscellaneous 65. Denver, CO: Historic Denver, Inc, 1997. Osterwald, Doris B. Rocky Mountain Splendor: A Mile by Mile Guide for Rocky Mountain National Park. 1st ed. Lakewood, CO: Western Guideways, 1989. Raup, Omer B. Geology along Trail Ridge Road: Rocky Mountain National Park Colorado. Estes Park, CO: Rocky Mountain Nature Association, 2005. Reed, Jack, and Gene Ellis. Rocks Above the Clouds: A Hiker’s and Climber’s Guide to Colorado Mountain Geology. The Colorado Mountain Club, n.d. Taylor, Andrew M. Guide to the Geology of Colorado. Golden, CO: Cataract Lode Mining Co., 1999.
Links ON-004-02 — Colorado POGI Map — Reviving this popular map of Colorado Points of Geologic Interest was a high priority, and here it is as a shared Google Map. Comments welcome! CGS Field trip guides: Birkeland, Peter W., Daniel C. Miller, Penny E. Patterson, Alan B. Price, and Ralph R. Shroba. “OF-96-04-27 Soil-Geomorphic Relationships near Rocky Flats, Boulder and Golden, Colorado Area with a Stop at the Pre-Fountain Paleosol of Wahlstrom.” Fieldtrip. Open File Report. Denver, CO: Colorado Geological Survey, Division of Minerals and Geology, Department of Natural Resources, 1996. Blair, Rob. “OF-96-04-09 Geology of the Western San Juan Mountains and a Tour of the San Juan Skyway, Southwestern Colorado.” Fieldtrip. Open File Report. Denver, CO: Colorado Geological Survey, Division of Minerals and Geology, Department of Natural Resources, 1996. Collins, Donna Bishop. “SP-27 Scenic Trips into Colorado Geology.” Touristic Geology, 1:250,000. Special Publication. Denver, CO: Colorado Geological Survey, Department of Natural Resources, 1985. Colorado Geological Survey. “OF-96-04-20 History, Geology, Hydrogeology, Summitville Mine and Downstream Effects, and Other Nearby Mines of the San Luis Valley, Colorado.” Fieldtrip. Open File Report. Denver, CO: Colorado Geological Survey, Division of Minerals and Geology, Department of Natural Resources, 1996. ———. “RockTalk V02N1, January 1999 – Annual Review.” RockTalk, January 1999. ———. “RockTalk V11N1, Spring 2008 – 2007 Summary.” RockTalk, Spring 2008. Erslev, Eric A., and Joe D. Gregson. “OF-96-04-25 Oblique Laramie Convergence in the Northeastern Front Range: Regional Implications for the Analysis of Minor Faults.” Fieldtrip. Open File Report. Denver, CO: Colorado Geological Survey, Division of Minerals and Geology, Department of Natural Resources, 1996. Fleming, Robert W., Rex L. Baum, and William Z. Savage. “OF-96-04-11 The Slumgullion Landslide, Hindsdale County, Colorado.” Fieldtrip. Open File Report. Denver, CO: Colorado Geological Survey, Division of Minerals and Geology, Department of Natural Resources, 1996. Henry, Thomas W., Emmett Evanoff, Daniel Grenard, Herbert W. Meyer, and Jeffrey A. Pontius. “OF-96-04-24 Geology of the Gold Belt Backcountry Byway, South Central Colorado.” Fieldtrip. Open File Report. Denver, CO: Colorado Geological Survey, Division of Minerals and Geology, Department of Natural Resources, 1996. Hynes, Jeffrey L. SP-31 Proceedings of the 1985 Conference on Coal Mine Subsidence in the Rocky Mountain Region. Special Publications, SP-31. Denver, CO: Colorado Geological Survey, Department of Natural Resources, 1986. Kirkham, Robert M., Bruce Bryant, Randall K. Streufert, and Ralph R. Shroba. “OF-96-04-08 Geology and Geologic Hazards of the Glenwood Springs Area, Central Colorado.” Fieldtrip. Open File Report. Denver, CO: Colorado Geological Survey, Division of Minerals and Geology, Department of Natural Resources, 1996. Krutak, Paul R. “OF-96-04-23 Depositional Environments of Codell-Juana Lopez Sandstones and Regional Structure and Stratigraphy of Canon City and Huerfano Areas and Northern Raton Basin, South-Central Colorado.” Fieldtrip. Open File Report. Denver, CO: Colorado Geological Survey, Division of Minerals and Geology, Department of Natural Resources, 1996. Matthews, Vincent and Colorado Geological Survey. “SP-57 Tourist Guide to Colorado Geology.” Special Publication. Denver, CO: Colorado Geological Survey, Department of Natural Resources, 2009. Matthews, Vincent, Katie KellerLynn, and Betty Fox, eds. SP-52 Messages in Stone: Colorado’s Colorful Geology. Second. Special Publications, SP-52. Denver, CO: Colorado Geological Survey, Department of Natural Resources, 2009. Noe, D. C., Jonathan L. White, and G. Zabel. “SP-56 Geology and Geologic Hazards along the I-70 Corridor, Vail to Glenwood Springs, Colorado.” In Field Trip Guidebooks, 1st North American Landslide Conference, edited by Jeffrey A. Coe and D. C. Noe. Special Publication, SP-56. Denver, CO: Colorado Geological Survey, Department of Natural Resources, 2007. Penn, Brian S., and David A. Lindsey. “OF-96-04-28 Tertiary Igneous Rocks and Laramide Structure and Stratigraphy of the Spanish Peaks Region, South-Central Colorado: Road Log and Descriptions from Walsenburg to La Veta to Aguilar.” Fieldtrip. Open File Report. Denver, CO: Colorado Geological Survey, Division of Minerals and Geology, Department of Natural Resources, 1996. Schwochow, Stephen D., ed. RS-08 Proceedings of the Fifteenth Forum on Geology of Industrial Minerals – Industrial Minerals in Colorado and the Rocky Mountain Region. Resource Series, RS-08. Denver, CO: Colorado Geological Survey, Department of Natural Resources, 1980. “SP-19 Colorado Tectonics, Seismicity and Earthquake Hazards: Proceedings and Field Trip Guide of a Symposium Held in Denver, Colorado, June 4-6, 1981.” Tectonics, Seismicity, and Earthquake. Special Publication. Denver, CO: Colorado Geological Survey, Department of Natural Resources, 1981. Thompson, Ren A., Mark R. Hudson, and C. L. Pillmore, eds. SP-44 Geologic Excursions to the Rocky Mountains and beyond: Field Trip Guidebook for the 1996 Annual Meeting, Geological Society of America, Denver, Colorado, October 28-31. Special Publications, SP-44. Denver, CO: Colorado Geological Survey, Department of Natural Resources, 1996. White, Jonathan L., N. C. Dessenberger, W. L. Ellis, J. D. Higgins, and S. Gaffney. SP-56 First North American Landslide Conference Field Trips, Vail, Colorado, June 3-10, 2007. Edited by D. C. Noe and Jeffrey A. Coe. Special Publication, SP-56. Denver, CO: Colorado Geological Survey, Department of Natural Resources, 2007. ———. “SP-56 Geology and Geologic Hazards along the I-70 Corridor, Glenwood Springs to Grand Junction, Colorado.” In Field Trip Guidebooks, 1st North American Landslide Conference, edited by D. C. Noe and Jeffrey A. Coe. Special Publication, SP-56. Denver, CO: Colorado Geological Survey, Department of Natural Resources, 2007.
ON-004-02 — Colorado POGI Map — Reviving this popular map of Colorado Points of Geologic Interest was a high priority, and here it is as a shared Google Map. Comments welcome! CGS Field trip guides: Birkeland, Peter W., Daniel C. Miller, Penny E. Patterson, Alan B. Price, and Ralph R. Shroba. “OF-96-04-27 Soil-Geomorphic Relationships near Rocky Flats, Boulder and Golden, Colorado Area with a Stop at the Pre-Fountain Paleosol of Wahlstrom.” Fieldtrip. Open File Report. Denver, CO: Colorado Geological Survey, Division of Minerals and Geology, Department of Natural Resources, 1996. Blair, Rob. “OF-96-04-09 Geology of the Western San Juan Mountains and a Tour of the San Juan Skyway, Southwestern Colorado.” Fieldtrip. Open File Report. Denver, CO: Colorado Geological Survey, Division of Minerals and Geology, Department of Natural Resources, 1996. Collins, Donna Bishop. “SP-27 Scenic Trips into Colorado Geology.” Touristic Geology, 1:250,000. Special Publication. Denver, CO: Colorado Geological Survey, Department of Natural Resources, 1985. Colorado Geological Survey. “OF-96-04-20 History, Geology, Hydrogeology, Summitville Mine and Downstream Effects, and Other Nearby Mines of the San Luis Valley, Colorado.” Fieldtrip. Open File Report. Denver, CO: Colorado Geological Survey, Division of Minerals and Geology, Department of Natural Resources, 1996. ———. “RockTalk V02N1, January 1999 – Annual Review.” RockTalk, January 1999. ———. “RockTalk V11N1, Spring 2008 – 2007 Summary.” RockTalk, Spring 2008. Erslev, Eric A., and Joe D. Gregson. “OF-96-04-25 Oblique Laramie Convergence in the Northeastern Front Range: Regional Implications for the Analysis of Minor Faults.” Fieldtrip. Open File Report. Denver, CO: Colorado Geological Survey, Division of Minerals and Geology, Department of Natural Resources, 1996. Fleming, Robert W., Rex L. Baum, and William Z. Savage. “OF-96-04-11 The Slumgullion Landslide, Hindsdale County, Colorado.” Fieldtrip. Open File Report. Denver, CO: Colorado Geological Survey, Division of Minerals and Geology, Department of Natural Resources, 1996. Henry, Thomas W., Emmett Evanoff, Daniel Grenard, Herbert W. Meyer, and Jeffrey A. Pontius. “OF-96-04-24 Geology of the Gold Belt Backcountry Byway, South Central Colorado.” Fieldtrip. Open File Report. Denver, CO: Colorado Geological Survey, Division of Minerals and Geology, Department of Natural Resources, 1996. Hynes, Jeffrey L. SP-31 Proceedings of the 1985 Conference on Coal Mine Subsidence in the Rocky Mountain Region. Special Publications, SP-31. Denver, CO: Colorado Geological Survey, Department of Natural Resources, 1986. Kirkham, Robert M., Bruce Bryant, Randall K. Streufert, and Ralph R. Shroba. “OF-96-04-08 Geology and Geologic Hazards of the Glenwood Springs Area, Central Colorado.” Fieldtrip. Open File Report. Denver, CO: Colorado Geological Survey, Division of Minerals and Geology, Department of Natural Resources, 1996. Krutak, Paul R. “OF-96-04-23 Depositional Environments of Codell-Juana Lopez Sandstones and Regional Structure and Stratigraphy of Canon City and Huerfano Areas and Northern Raton Basin, South-Central Colorado.” Fieldtrip. Open File Report. Denver, CO: Colorado Geological Survey, Division of Minerals and Geology, Department of Natural Resources, 1996. Matthews, Vincent and Colorado Geological Survey. “SP-57 Tourist Guide to Colorado Geology.” Special Publication. Denver, CO: Colorado Geological Survey, Department of Natural Resources, 2009. Matthews, Vincent, Katie KellerLynn, and Betty Fox, eds. SP-52 Messages in Stone: Colorado’s Colorful Geology. Second. Special Publications, SP-52. Denver, CO: Colorado Geological Survey, Department of Natural Resources, 2009. Noe, D. C., Jonathan L. White, and G. Zabel. “SP-56 Geology and Geologic Hazards along the I-70 Corridor, Vail to Glenwood Springs, Colorado.” In Field Trip Guidebooks, 1st North American Landslide Conference, edited by Jeffrey A. Coe and D. C. Noe. Special Publication, SP-56. Denver, CO: Colorado Geological Survey, Department of Natural Resources, 2007. Penn, Brian S., and David A. Lindsey. “OF-96-04-28 Tertiary Igneous Rocks and Laramide Structure and Stratigraphy of the Spanish Peaks Region, South-Central Colorado: Road Log and Descriptions from Walsenburg to La Veta to Aguilar.” Fieldtrip. Open File Report. Denver, CO: Colorado Geological Survey, Division of Minerals and Geology, Department of Natural Resources, 1996. Schwochow, Stephen D., ed. RS-08 Proceedings of the Fifteenth Forum on Geology of Industrial Minerals – Industrial Minerals in Colorado and the Rocky Mountain Region. Resource Series, RS-08. Denver, CO: Colorado Geological Survey, Department of Natural Resources, 1980. “SP-19 Colorado Tectonics, Seismicity and Earthquake Hazards: Proceedings and Field Trip Guide of a Symposium Held in Denver, Colorado, June 4-6, 1981.” Tectonics, Seismicity, and Earthquake. Special Publication. Denver, CO: Colorado Geological Survey, Department of Natural Resources, 1981. Thompson, Ren A., Mark R. Hudson, and C. L. Pillmore, eds. SP-44 Geologic Excursions to the Rocky Mountains and beyond: Field Trip Guidebook for the 1996 Annual Meeting, Geological Society of America, Denver, Colorado, October 28-31. Special Publications, SP-44. Denver, CO: Colorado Geological Survey, Department of Natural Resources, 1996. White, Jonathan L., N. C. Dessenberger, W. L. Ellis, J. D. Higgins, and S. Gaffney. SP-56 First North American Landslide Conference Field Trips, Vail, Colorado, June 3-10, 2007. Edited by D. C. Noe and Jeffrey A. Coe. Special Publication, SP-56. Denver, CO: Colorado Geological Survey, Department of Natural Resources, 2007. ———. “SP-56 Geology and Geologic Hazards along the I-70 Corridor, Glenwood Springs to Grand Junction, Colorado.” In Field Trip Guidebooks, 1st North American Landslide Conference, edited by D. C. Noe and Jeffrey A. Coe. Special Publication, SP-56. Denver, CO: Colorado Geological Survey, Department of Natural Resources, 2007.
Media Zoom Download Image Share Panorama of the San Juan Mountains, Summer Coon Volcano, Saguache County. Photo credit: Emily Perman (CGS).