Intro Blown across the land by wind or carried along by water and ice as the land continued to remake itself, loose sediments eventually compressed and cemented into rock and left messages in stone for us to decipher. Sediments include the mud at the bottom of streams, the sand dunes at the foot of the mountains, the chemical precipitates of salt in shallow seas, the beaches at the edge of inland seas, and the graveyards of tiny fossils at the bottom of tropical oceans. In these sedimentary layers, such as the Book Cliffs in western Colorado, the imprints of changing life forms in an ancient world are faithfully recorded. Details Sediments that were originally particles of rock or former living organisms were transported and later sculpted by wind and water, pressed, and finally lifted to prominence as some of the state’s most imposing landmarks. The sandstones of Colorado National Monument, the reddish-brown siltstones and mudstones of Owl Canyon, and the Flatirons that flank Boulder are all sedimentary rocks. Other sedimentary deposits include massive limestone formations around Leadville, the evaporites of the Eagle Valley, chalks of the eastern plains, coals near Trinidad, oil shale in western Colorado, and the thick shale of eastern Colorado. Honeycombed “tafoni” weathering in sandstone, Iles Formation, Lower Hayden Gulch in Routt County, Colorado. Photo credit: Dave Noe for the CGS. The Flatirons overlooking Boulder, Colorado are comprised of once flat-lying Permian Fountain Formation sedimentary rock that were tilted to 50 degrees by the orogenic uplift of the Rocky Mountains. Photo credit: Vince Matthews for the CGS. Drill-pad for shot-holes, Seneca II-W Coal Mine, Routt County, Colorado, October 2005. Photo credit: Chris Carroll for the CGS. Figure 03. Highly contorted sedimentary strata in the evaporitic terrain between Gypsum and Glenwood Springs, Colorado, seen along the I-70 corridor, April 2012. Photo credit: Jon White for the CGS. A section of eolian sand at a construction excavation in the southern part of the La Salle quad, Weld County, Colorado, July 2018. Eolian deposits, composed of sand and/or loess, comprise the surface deposits of much of Eastern Colorado. Photo credit: Martin Palkovic for the CGS. An exposure of the Triassic Dolores Formation in a road cut on the east side of the Lemon Reservoir dam on the Florida River in La Plata County, Colorado, May 2019. Beds are dipping south along the Hogback Monocline that separates the San Juan Basin to the south from the San Juan Dome to the north. Here the fluvial sediments consist of interbedded sandstone, siltstone, and mudstone with sandstone dominating. Although not recognized as a major aquifer the sandstone can carry groundwater and at this location water is seeping out through fractures. Photo credit: Peter Barkmann for the CGS. How do geologists know that a particular sedimentary rock formed in a specific environment? In 1795 geologist Sir Charles Lyell developed a concept that is the next best thing to being there: “The present is the key to the past.” The idea is that by studying the characteristics found in modern depositional environments and comparing them to similar features found in ancient rocks, one can solve the mystery. For example, in Colorado, we can study the features of modern dunes in the Great Sand Dunes National Park and compare them to the ancient deposits of the 250 million-year-old Lyons sandstone found along the eastern flank of the Front Range. Using the same theory allows us to decipher the rock in the images below to be mudcracks, ripple marks, coarse-grained conglomerate, and raindrop impressions. Fossilized mudcracks in the Mesa Verde Formation near Paonia Reservoir, Gunnison County, Colorado. Photo credit: CGS. Ripple marks in the Dakota sandstone, Dinosaur Ridge, near Morrison, Colorado. Photo credit: CGS. Detail of bedding above Sage Creek coal at the Seneca II-W mine in Routt County, Colorado, October 2005. Photo credit: Chris Carroll for the CGS.
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 Red Rocks Park and Amphitheatre, Jefferson County. Photo credit: F Scot Fitzgerald (CGS). Zoom Download Image Share Honeycombed "tafoni" weathering in sandstone, Iles Formation, Lower Hayden Gulch in Routt County, Colorado. Photo credit: Dave Noe for the CGS. Zoom Download Image Share The Flatirons overlooking Boulder Zoom Download Image Share Drill-pad for shot-holes, Seneca II-W Coal Mine, Routt County, Colorado, October 2005. Photo credit: Chris Carroll for the CGS. Zoom Download Image Share Figure 03. Highly contorted sedimentary strata in the evaporitic terrain between Gypsum and Glenwood Springs Zoom Download Image Share A section of eolian sand at a construction excavation in the southern part of the La Salle quad, Weld County, Colorado, July 2018. Eolian deposits, composed of sand and/or loess, comprise the surface deposits of much of Eastern Colorado. Photo credit: Martin Palkovic for the CGS. Zoom Download Image Share An exposure of the Triassic Dolores Formation in a road cut on the east side of the Lemon Reservoir dam on the Florida River in La Plata County, Colorado, May 2019. Beds are dipping south along the Hogback Monocline that separates the San Juan Basin to the south from the San Juan Dome to the north. Here the fluvial sediments consist of interbedded sandstone, siltstone, and mudstone with sandstone dominating. Although not recognized as a major aquifer the sandstone can carry groundwater and at this location water is seeping out through fractures. Photo credit: Peter Barkmann for the CGS. Zoom Download Image Share Fossilized mudcracks in the Mesa Verde Formation near Paonia Reservoir, Gunnison County, Colorado. Photo credit: CGS. Zoom Download Image Share Ripple marks in the Dakota sandstone, Dinosaur Ridge, near Morrison, Colorado. Photo credit: CGS. Zoom Download Image Share Detail of bedding above Sage Creek coal at the Seneca II-W mine in Routt County, Colorado, October 2005. Photo credit: Chris Carroll for the CGS.