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Webpage Overview

This website is intended to provide a starting point for those interested in learning more about riverine processes and landforms in the Colorado Front Range. We have tried to provide a broad overview of a range of diverse information, as well as citations or links to more specific information. We will continue to develop the website with time, and we would like to hear about aspects that you find useful, difficult to use or understand, or missing or erroneous information. Please direct all comments to Ellen Wohl, Department of Geosciences, Colorado State University ellenw@warnercnr.colostate.edu or fill out our questionnaire.

Description of Colorado Front Range

The Colorado Front Range is the portion of the Rocky Mountains in the State of Colorado extending from the Wyoming border on the north 300 km to the drainage divide between the South Platte and Arkansas Rivers on the south, and from the Continental Divide on the west to the base of the mountains at approximately 1500 m elevation on the east. The Front Range is drained by the headwater channels of the South Platte River basin; from north to south, the major channels are the Poudre River, Big Thompson River, St. Vrain Creek, Clear Creek, and Upper South Platte River.

Folding and faulting occurred during Laramide uplift (80-35 million years ago) of the Front Range, which elevated approximately 3 km of Paleozoic and Mesozoic sedimentary rocks and underlying Precambrian crystalline rocks (Bradley 1987). Subsequent erosion has mostly removed the sedimentary rocks, leaving Precambrian-age granites, gneiss, and schist as the core of the Front Range (Tweto 1979). The Front Range has been relatively tectonically quiescent since the early Tertiary (Crowley et al. 2002; Anderson et al. 2006). Pleistocene valley glaciers extended down to approximately 2300 m elevation (Madole et al. 1998). Narrow, glaciated spines form the range crests at 4000 m elevation, below which lie widespread surfaces of low relief at 2000-3000 m elevation, with deeply incised fluvial canyons. The downstream portions of the fluvial canyons are more deeply incised than the portions upstream from an inflection point in the longitudinal profile. Incision of the South Platte River has driven exhumation of the Denver Basin, at the eastern border of the Front Range, during the past few million years. Anderson et al. (2006) accurately simulated the longitudinal profile of Boulder Creek by assuming that fluvial incision is proportional to stream power and is on the order of 0.15 mm/yr.

The elevational and climatic diversity of the Front Range support diverse communities of terrestrial vegetation, from semiarid steppe at the base of the range to alpine tundra at the highest elevations. Basic vegetation zones are the (i) alpine zone (approximately 4300-3500 m elevation), (ii) subalpine zone (approx. 3500-2500 m) that includes Engelmann spruce (Picea engelmannii), subalpine fir (Abies lasiocarpa), lodgepole pine (Pinus contorta), aspen (Populus tremuloides), and limber pine (Pinus flexilis), and (iii) montane zone (approx. 2500-1500 m) that includes ponderosa pine (Pinus ponderosa) and Douglas-fir (Pseudotsuga menziesii) (Veblen and Donnegan 2005).

See the webpage on Hydroclimatology for a description of climate and streamflow in the Front Range.

Much of the land within the Front Range lies with the Arapaho-Roosevelt or Pike-San Isabel National Forests and Rocky Mountain National Park and is covered in forests that have regrown since widespread deforestation during the late 19th century (see Land Use History). Many cities with a population of 10,000 or less lie within the Front Range, but the major regional population centers are immediately east of the Front Range. Major transportation corridors tend to follow river valleys.

Poudre river unglaciated confined reach

(Photo by E. Wohl)

Location of Colorado Front Range

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The Colorado Front Range can be subdivided into 6 major drainage basins: Cache la Poudre, Big Thompson, St. Vrain River, Clear Creek, Upper South Platte and South Platte Headwaters. Click on the map of the Colorado Front Range to learn more about each watershed.

Front Range with Roads Big Thompson Link to Saint Vrain Creek Page Link to Clear Creek Page Link to Upper South Platte Page Link to South Platte Headwaters Page

(Maps created by E. Carlson, 2008)

Variability of Valley Bottoms in Colorado Front Range

The sources of varibility that effect valley bottoms of the Colorado Front Range include climatic variability, hillslope influences (e.g. fire and biodisturbance) anthropomorphic disturbance (e.g. beaver-trapping, timber harvest, placer-mining, tie-drivers, flow regulation, etc.), and flooding. The influence of each of these disturbances can vary based on both channel and valley characteristics. The concept of geomorphic process domains reflects how spatial variability in geomorphic processes governs temporal patterns of disturbances that influence ecosystem structure and dynamics (Montgomery, 1999). For example, spatial differences in flood magnitude and frequency, which exists in the Colorado Front Range, can be used to differentiate boundaries between distinct process domains. Above approximately 2300 m elevation in the Front Range, high flows occur regularly each spring and early summer in association with snowmelt runoff. Snowmelt runoff creates flooding at lower elevations, but late summer convective storms can also create rainfall flooding at elevations below approximately 2300 m. Rainfall-generated flash floods have much greater magnitude for a given drainage area, and occur more rapidly and unpredictably. The upper elevation limit for flash flooding corresponds relatively well with the lower elevation limit for Pleistocene-age valley glaciers in the Front Range.

Differences in flood hydroclimatology and fluvial versus glacial morphology in relation to elevation support the differentiation of process domains in the Front Range. We propose that eight process domains exist in the Colorado Front Range along valley bottoms, i.e., colluvial hollows, ephemeral channels, glaciated confined, glaciated partially confined, glaciated unconfined, unglaciated confined, unglaciated partially confined, unglaciated unconfined. The names of individual process domains reflect dominant characteristics. ‘Glaciated’ indicates areas above 2300 m elevation, and ‘unglaciated’ indicates areas below 2300 m elevation. ‘Confined’ refers to valley-bottom segments that are relatively narrow and steep, whereas ‘unconfined’ valley bottoms are much wider than the active channel. For each of these process domains different responses are expected for different disturbances. The expected response to each type of disturbance is described under the process domains tab and under each drainage basin.


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