Geotimes - April 2003

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Geomedia

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Maps:
Mapping Colorado
U.S. Geological Survey maps

Maps
Mapping Colorado

Currently, only 24 percent of Colorado’s spectacular geology has been mapped at the fine scale of 1:24,000. At the same time, the state hosts many geologic hazards. Most maps of Colorado are at much broader scales, failing to show detail of basic geology crucial to safe engineering and building practices in a state that had the third-fastest-growing population during the 1990s. And the 2000 Census showed that the state, despite some economic woes, remains one of the fastest growing.

Detailed geologic maps also aid the mineral industries that help fuel such growth.

Since 1992, the Colorado Geological Survey (CGS) has mapped 1:24,000-scale quadrangles in high-impact areas under the STATEMAP component of the National Cooperative Geologic Mapping Program. In 2002, CGS completed its 43rd geologic quadrangle map. The long-range plan for the state is to complete 116 high-priority quadrangles in the next 15 years.

The survey’s approach is to select rapidly growing areas with relatively high potential for hazards and map contiguous quadrangles.

In addition to mapping bedrock, CGS geologists have mapped the Quaternary deposits at the surface. Understanding these deposits is extremely important for implementing sound engineering practices because of potential for subsidence and landslides.

The CGS mapping has not only yielded information about potential hazards, but also advanced scientific understanding of the state, offering information about:

the age of incision of the Colorado River,
the existence of a regional evaporate collapse area,
the chronology of late Cenozoic basaltic volcanism,
the existence of talus flatiron rings,
the location of previously unrecognized Quaternary faults,
the location of a mountain-front fault,
the detailed stratigraphy of an important aquifer;
the discovery of a new conglomerate unit;
the location of a previously unrecognized Ancestral Rockies fault; and
structural understanding of the Rampart Range fault.

Completed maps under this program include 12 in the Glenwood Springs area, eight in the Durango area, 10 in the Colorado Springs area, five in the Salida area and five in the central mountains.

Recently Published Geologic Maps from the Colorado Geological Survey Open File Series include:

OF00-03. Geologic Map of the Colorado Springs Quadrangle, El Paso County, Colorado by C.J. Carroll and T.A. Crawford, 2000. Includes cross section, map unit correlation, shaded-relief map with geology overlay, booklet of extended descriptions of map units, economic geology and selected references. Specify standard map or full shaded relief map when placing an order. Seventeen pages. One color plate (1:24,000). $10.

OF01-05. Geologic Map of Georgetown Quadrangle, Clear Creek County, Colorado by B.L. Widmann and U. Miersemann, 2002. Includes cross section, map unit correlation, shaded-relief map with overlay, booklet of extended descriptions of map units, geologic hazards, structural ore deposits and alteration products, color plate (1:24,000). $10.

OF99-07. Geologic Map of the Mt. Sopris Quadrangle, Garfield and Pitkin Counties, Colorado by R.K. Streufert, 1999. Includes cross section, map unit correlation, shaded-relief map with geology overlay, booklet of extended descriptions of map units, geologic setting, structural geology, economic geology and references. Twenty-one pages. One color plate (1:24,000). $10.

OF99-04 Geologic Map of the Durango West Quadrangle, La Plata County, Colorado by R.M. Kirkham and others, 1999. Includes cross section, map unit correlation, shaded-relief map with geology overlay, booklet of extended descriptions of map units, fracture data and analysis, mineral and energy resources and references. Thirty-four pages. One color plate (1:24,000). $10.

A complete list of available maps and how to order them is online.

Other new maps from the U.S. Geological Survey are:

All the maps listed below are available for $20 from USGS Information Services or free online.

MF-2402. CALIFORNIA. Geologic map and map database of western Sonoma, northernmost Marin, and southernmost Mendocino Counties, California by M.C. Blake Jr., R.W. Graymer and R.E. Stamski. 2002. Scale 1:100,000. One color sheet with 43-page text. Online.

MF-2404. New Mexico. Geologic map of the Bernalillo NW quadrangle, Sandoval County, New Mexico by D.J. Koning and S.F. Personius. 2002. Scale 1:24,000. One color sheet. Online.

MF-2405. New Mexico. Geologic map of the Santa Ana Pueblo quadrangle, Sandoval County, New Mexico by S.F. Personius. 2002. Scale 1:24,000. One color sheet. Online.

MF-2408. Alaska. Surficial geologic map of the Hughes quadrangle, Alaska by T.D. Hamilton. 2002. Scale 1:250,000. One color sheet with eight-page text. Online.

MF-2409. Alaska. Surficial geologic map of the Bettles quadrangle, Alaska by T.D. Hamilton. 2002. Scale 1:250,000. One color sheet with eight-page text. Online.

To order USGS maps, contact USGS Information Services, P.O. Box 25286, Denver, CO, 80225. Phone: 888/ASK-USGS (888/275-8747).

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Randall Orndorff compiles the Maps section and is the associate program coordinator for the USGS National Cooperative Geologic Mapping Program. E-mail him at rorndorf@usgs.gov.

The author thanks Vince Matthews of the Colorado Geological Survey for contributing to this story.

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