Jun 272017
OF-16-02 Geologic Map of the Watkins Quadrangle, Arapahoe and Adams Counties, Colorado

We’ve just uploaded the next of our free STATEMAP quadrangle map products to our online store: the Geologic Map of the Watkins Quadrangle, Arapahoe and Adams Counties, Colorado. The STATEMAP series in general provides a detailed description of the geology, mineral and ground-water resource potential, and the geologic hazards of an area. Digital PDF/ZIP download.

Location of the Watkins Quadrangle, Arapahoe and Adams Counties, Colorado.

Location of the Watkins Quadrangle, Arapahoe and Adams Counties, Colorado.

Matt Morgan, Senior Research Geologist and CGS Deputy Director, along with Senior Engineering Geologist (Emeritus) Jon White generated this map with special input from Richard Madole (surficial geology) and Shannon Mahan (OSL analysis), both of the USGS. This free release from the CGS includes two PDF plates (with a geologic map, cross-section with correlation, oblique 3D view, and legend) along with the corresponding GIS data package that allows for digital viewing, all in a single ZIP file.

This mapping project was funded jointly by the U.S. Geological Survey through the STATEMAP component of the National Cooperative Geologic Mapping Program, which is authorized by the National Geologic Mapping Act of 1997, and also by the CGS using the Colorado Department of Natural Resources Severance Tax Operational Funds. The CGS matching funds come from the severance paid on the production of natural gas, oil, coal, and metals. Geologic maps produced through the STATEMAP program are multi-purpose information sources useful for land-use planning, geotechnical engineering, geologic-hazard assessment, mineral-resource development, and ground-water exploration.

This particular 7.5-minute, 1:24,000 quadrangle is situated within the Denver Basin, a Laramide-age structural basin that is an important resource for water along with oil & gas. Growth of the Denver Metro area is occurring in the northern half of the quadrangle which is crossed by Interstate 70 and is minutes from Denver International Airport. Dips within the quadrangle typically range from 3° to 7° to the N-NE which reflects the regional structural dip of the basin. Bedrock units consist of the lower part of the Dawson Arkose and the Denver Formation. The widespread Dawson Arkose is white to tan in color and composed of cross-bedded arkoses, pebbly arkoses and arkosic pebble conglomerates with sparse claystone and siltstone beds. The arkoses were shed off the uplifting Front Range into the subsiding Denver Basin during the latter phases of the Laramide Orogeny. Cobble-rich conglomeratic lenses were recognized in the lower part of the Dawson Arkose and represent localized flooding events in a typically quiet fluvial environment. The Denver Formation is finer grained, more clay rich, and yellower in color than the overlying Dawson Arkose and is part of a low-energy alluvial plain environment also related to the Laramide. The units are separated by a basin-wide, yet occasionally discontinuous variegated paleosol that is a regional unconformity and an important time-stratigraphic marker at the Paleocene-Eocene boundary.

Surficial deposits consist of middle Pleistocene to Holocene flood-plain and terrace-forming alluviums and Holocene sand deposits of predominantly eolian origin. The sand deposits are composed of disaggregated sediments derived from the weathering and subsequent mobilization of the underlying Dawson Arkose. New Optically Stimulated Luminescence (OSL) ages, collected during this project, indicate that these eolian deposits were first active during the lowermost Holocene. High-level gravel deposits of Neogene-early Quaternary age cap isolated buttes in the southern half of the quadrangle. These gravels consist of cobbles and boulders of granite, quartzite, sandstone and tuffaceous igneous rocks and were likely derived from the erosion of the late Eocene Castle Rock Conglomerate.

Citation: Morgan, Matthew L., and Jonathan L. White. “OF-16-02 Geologic Map of the Watkins Quadrangle, Arapahoe and Adams Counties, Colorado” Geologic. Open File Reports. Golden, CO: Colorado Geological Survey, 2016.
Feb 062017

With all the precipitation in the Rockies this year (we’re at +153% normal snowpack at the moment), we thought we would re-release a publication that highlights at least one important aspect of Colorado snowfall — that is, the significant danger of avalanches. The Snowy Torrents: Avalanche Accidents in the United States 1980-86, compiled and written by Nick Logan and Dale Atkins and illustrated with Larry Scott’s fine pencil drawings, was first published in 1996. We still have a few hard-copies available and, because of that, yes, we do charge for the PDF download. However, Larry went back and re-made the PDF from the original publication file, producing a file that is far better than the rather poor digital scan we had offered previously.

The volume details 146 oft-times harrowing stories surrounding avalanches, the lives they claim, survivors and witnesses, along with assessments as to what happened, why it happened, and what could have been done to prevent loss of life and/or property. The authors are never judgmental, and their clear-eyed accounts contain a wealth of wisdom that will add to the knowledge-base of any winter backcountry enthusiast.

Citation: Logan, Nick, and Dale Atkins. SP-39 The Snowy Torrents: Avalanche Accidents in the United States, 1980–86. Special Publications 39. Denver, CO: Colorado Geological Survey, Department of Natural Resources, 1996.
Jan 112017

Regarding the Colorado Geological Survey (an article appearing in the Mining Reporter, March 1907):

We note that one of our contemporaries, in recently commenting on the University bill creating a State Geological Survey of Colorado — the bill reported favorably on by the joint Senate and House mining committee — voices in no uncertain language its regret at the “truly pitiable outcome of the effort to establish a Geological Survey of Colorado.” In a lengthy and well-written editorial, criticism is made of the proposed advisory board, particularly of the placing thereon of the presidents of the State University and the State Agricultural College; also, having the survey located at Boulder instead of Denver; of the naming as state geologist, the professor of geology of the State University, who may be a good teacher, but who, like the majority, may or may not be an effective executive; and lastly, of the paltry appropriation of $5,000 annually for this important work in a state productive of $50,000,000 and more yearly.

Exception is also taken to the naming of state institution teachers as assistants to the State Geologist, who ought to have the assistance of men less academic and having a knowledge of the exploitation of ore deposits and of the search for them.

This editorial expression, coming from a former Coloradoan, is worthy of consideration. It is in accord, in large part, with our own views, as our readers know. In addition to the criticisms made by our contemporary, we would like to emphasize another objectionable feature in this favorably reported bill, viz., the naming of any one as state geologist who is not to devote his entire time to the survey work. — from the Mining Reporter, vol. LV, March 28, 1907, no. 13, Denver, Colorado.

We’re happy to say that our current efforts to provide professional geologic information to the residents of Colorado far exceed the original scope of responsibilities and possibilities of the Territorial Geologist. But like those old-time miners, walking the mountains of this beautiful state, we also share a real passion for what we are doing.

You can find an in-depth history of the Survey and its 1872-legislated precursor, the office of Territorial Geologist, in IS-27 History of The Colorado Geological Survey (1872-1988), a free PDF download at our bookstore.

Citation: Rold, J. W., and S. D. Schwochow. IS-27 History of The Colorado Geological Survey (1872-1988). Information Series, IS-27. Denver, CO: Colorado Geological Survey, Department of Natural Resources, 1989.