Karl Kellogg, Project Chief, Geology and Environmental Change Science Center, 303-236-1305
Terry Klein, Project Chief, Central Mineral Resources Team, 303-236-5605
The Front Range urban corridor in north-central Colorado, with a population growth of more than 30 percent since 1990, stretches about 350 km from Pueblo in the south, through Denver, north to the Colorado-Wyoming border. Important resource and land-use management issues throughout central Colorado, especially in the mountainous region west of the urban corridor, include:
A major goal of our completed integrated work was to revise existing geologic mapping and remap poorly understood areas in order to create state-of-the-art, digital databases at a level of detail appropriate for a series of 30' x 60' geologic quadrangles in and adjacent to the Front Range. Mapping and compilation was completed October, 2011. The Estes Park and Denver West quadrangles are published and the Bailey and Fort Collins quadrangles are in review. Several topical studies conducted concurrently with the mapping include:
Index map of the northern Front Range showing the location and status of 1:24,000-scale and 1:100,000-scale geologic mapping activities. (See Project Mapping for links to online maps)
The Denver West map (USGS Scientific Investigations Map 3000) was prepared from scanned images of published and unpublished geologic maps as well as new reconnaissance mapping. A significant contribution involves substantial new mapping of surficial features, including glacial limits, major Pleistocene debris flows near Boulder, and new interpretations of terrace deposits. An included booklet contains a detailed description of map units, an in-depth geologic history from the Proterozoic to the Quaternary, and a discussion of geologic hazards.
Geologic information was captured digitally from scanned images using Adobe Illustrator, with MAPublisher as an interface to register data in real-world coordinates. Shapefiles were then exported to ArcGIS to prepare the final map. The result is a GIS database that can be queried with respect to rock type or type of geologic deposit, or geologic age. Point data identifying abandoned mines and locations of samples collected for geologic ages and geochemical analyses will be added to the database.
Denver West, Colorado 1:100,000-scale geologic map. (USGS Scientific Investigations Map 3000)
Geology for the Estes Park sheet was compiled by Bill Braddock (USGS-deceased) and published as USGS Scientific Investigations Map 3039. The ArcInfo database incorporates detailed mapping in the Proterozoic core of the Front Range by Bill and many of his graduate students from the University of Colorado-Boulder, as well as other USGS mapping in the mountains and plains and information from numerous topical studies. The Estes Park sheet encompasses most of Rocky Mountain National Park, the growing communities of Boulder, Longmont, and Loveland, and the headwaters of the principal water supplies for these areas.
Estes Park Quadrangle, 1:100,000-scale geologic map. (USGS Scientific Investigations Map 3039)
The geology of the Fort Collins quadrangle spans the breadth of the Front Range south of the Wyoming state line, from the Laramie River valley on the west to the high plains around Fort Collins on the east. Compilation work began in 2004 and the completed map is now in review. Faculty at the University of Northern Colorado and at Southwest Missouri State College are collaborating on the 1:100,000-scale compilation.
The Fort Collins quadrangle highlights several important geologic themes that will be investigated during the project. Laramide deformation in the Laramie River Valley on the west appears to have involved eastward displacement of the southern Medicine Bow Range and westward displacement of the Front Range, leading to unresolved structural complexities in the Chambers Lake area.
View north along the Laramie River Valley, showing convergent Laramide thrusts bounding the ranges (Jim Cole photo)
The Cache la Poudre River, and several other major east-flowing streams, preserves large-wavelength meanders that are now deeply entrenched into the hard crystalline rocks of the range; these features indicate how the drainage network has adjusted to renewed uplift of the Front Range, probably during the Pliocene epoch. High-level gravel deposits are preserved on top of an older erosion surface that was abandoned during this more recent incision.
View west over the eastern part of the Cache la Poudre River canyon showing the old river course and the modern, entrenched meandering drainage (Bill Braddock photo)
Surficial deposits east of the mountain uplift reflect competing processes of river incision and aggradation, as well as the strong influence of wind during glacial-climate oscillations, all of which contribute to landforms (and resulting land-use conditions and limitations) around the growing community of Fort Collins.
Geologic hazards are common in the Denver West and Estes Park Quadrangles and new mapping will incorporate surficial deposits that reflect these hazards. Many hazards are related in part to building and road construction as well as to associated changes in land-use that enhances surface water runoff and locally promotes infiltration of surface water and locally destabilizes slopes. Removal and destruction of vegetation by human and natural processes—such as by land surface modification at construction sites and by dry climatic episodes and forest fires—promote slope instability. Mountain slopes are particularly susceptible to gullying and mass movement.
| Hazard | Plains | Hogback belt | Mountains |
|---|---|---|---|
| Stream flooding |  |
|
|
| Gullying | |
|
|
| Expansive soils and sediments | |
|
 |
| Heaving bedrock | |
|
|
| Debris-flow deposition | |
|
|
| Landslides and other types of mass movement | |
|
|
Extensive debris-flow deposits of at least three ages during the middle and early Pleistocene are common along the Flatirons (steep front of the Hogback belt) near Boulder, Colorado, where boulders 1-8 m long composed of the Fountain Formation have been transported by bouldery debris flows about 1.5-3 km east of their bedrock sources. In order to constrain the ages of these debris-flow deposits, we have sampled large boulders on one of the youngest extensive deposits for cosmogenic dating (26Al, 10Be, and 21Ne). Geologic relationships suggest that the youngest extensive debris-flow deposits may be about 0.15-0.25 Ma. Dating of these boulders will help us to evaluate the climatic conditions (periglacial or interglacial) that promote the formation of these deposits.
Large debris-flow boulder of Pennsylvanian Fountain Formation in lower Shadow Canyon near Boulder being sampled for cosmogenic dating.
View to north along Dakota hogback; town of Golden in middle distance. Golden fault cuts out Dakota Group rocks about 1 km north, although continuation of hogback can be seen about 5 km farther north. Interstate 70 road cut reveals spectacular reference section through upper Morrison Formation and Dakota Group rocks. North and South Table Mountains at right are capped by 64 Ma alkalic basalts of Denver Formation. Rock quarry in Lower Proterozoic gneiss is at left (as indicated).
NOTE: Any use of trade, product or firm names is for descriptive purposes only and does not imply endorsement by the U.S. Government.
U.S. Department of the Interior | U.S. Geological Survey
URL: http://gec.cr.usgs.gov/research/central_colorado/
Page Contact Information: GECSC Web Team
Page Last Modified: Tue 5-Jul-2011 9:22:52 MDT
