Landscape

High mountains of the Front Range form the northern and eastern borders of South Park, with the high point of Mount Evans reaching 4345 m elevation (figure 3.2). On the west the Mosquito Range forms a high and nearly unbroken chain of peaks greater than 4000 m elevation, reaching a high point on Mount Sherman and ending at the Buffalo Peaks (figure 3.3). The Front and Mosquito ranges supported localized ice caps and extensive valley glacier complexes during stades of the Pleistocene, as evidenced by the well-developed cirques and jagged peaks of the skyline. Lateral moraines are prominent on the sides of most large valleys, and in several areas lateral and dead ice moraines have created kettle pond complexes at the mountain front. Glaciers occurred in the Mosquito Range

FIGURE 3.1 Computer image of Colorado terrain, showing the four Colorado parks. The Great Plains are on the right, the Colorado Plateau is on the left, and the Rocky Mountains are in the center.

FIGURE 3.1 Computer image of Colorado terrain, showing the four Colorado parks. The Great Plains are on the right, the Colorado Plateau is on the left, and the Rocky Mountains are in the center.

FIGURE 3.2 Sketch map indicating the location of Porcupine Cave and the major features of South Park.

Latitude

FIGURE 3.2 Sketch map indicating the location of Porcupine Cave and the major features of South Park.

as far south as Buffalo Peaks, but they advanced no closer than 20 km to Porcupine Cave.

The melting of glacier ice created floods capable of moving large amounts of sediment down the mountain fronts, where alluvial fans, outwash plains, and braided rivers formed. Alluvial deposits extend as a blanket from the Mosquito Range east across the floor of South Park. Currently snowmelt from the mountains fills streams and percolates through outwash deposits, causing shallow groundwater to flow down into the interior of South Park.

Limestone and dolomite rocks of the Leadville Limestone formation are prominent in the Mosquito Range and have formed calcareous alluvial deposits. Surface water and ground-water flowing through the alluvium is alkaline, with pHs ranging from 6.5 to more than 8.0 in the region from Kenosha Pass to the South Fork of the South Platte River. The most abundant cations are calcium and magnesium, and the most abundant anion is bicarbonate.

From the South Fork of the South Platte River to the area of Antero Reservoir, the Minturn and Maroon formations outcrop along the western foothills of South Park or are bedded close to the ground surface and buried by outwash gravels. The Minturn Formation contains gypsum beds. Karst topography has formed in several areas, for example in the High Creek drainage, creating ponds (Appel, 1995). Groundwater discharging from these formations is highly saline. Large salt flats occur on the southern, western, and eastern sides of An-tero Reservoir, and the reservoir was built atop the greatest concentration of salt springs in Colorado. Salt Creek flows into Antero Reservoir from the southwest, where salt was commercially produced at the Salt Works Ranch in the late 1800s (Simmons, 1992). Surface water, groundwater, and soils contain high concentrations of sodium, sulfate, and chloride ions. A small natural lake located just north of Antero Reservoir is so saline that it never freezes. French fur trappers referred to this portion of South Park as Bayou Salade in the mid-nineteenth century owing to the widespread saline marshes (Fremont, 1887).

A section of the Front Range known as the Tarryall Mountains forms the northeastern side of South Park. The Tarryalls contain granite domes and few peaks higher than 3300 m elevation. Unlike higher-elevation portions of the Front and Mosquito ranges, the Tarryalls do not contain extensive highlands, and valley glaciers did not form there during the Pleistocene. The environment of South Park was certainly very different during glacial stades, but the presence of large

FIGURE 3.3 Looking southwest across the northern portion of South Park toward the Mosquito Range. In the foreground the abundant light-colored low plants are fringed sage, with blue grama grass. The darker areas on the valley floor in the distance are wetlands dominated by arctic rush. Conifer forests dominate the lower portions of the distant mountains, and alpine tundra occurs on the higher mountains.

FIGURE 3.3 Looking southwest across the northern portion of South Park toward the Mosquito Range. In the foreground the abundant light-colored low plants are fringed sage, with blue grama grass. The darker areas on the valley floor in the distance are wetlands dominated by arctic rush. Conifer forests dominate the lower portions of the distant mountains, and alpine tundra occurs on the higher mountains.

FIGURE 3.4 Winter view looking west to Silverheels Mountain just north of Fairplay. The alpine zone above the treeline has large windblown areas that support fell field vegetation and snowbeds. In the foreground the snowpack is light, with a snow accumulation area on the lee side of the fence in the middle distance and a thin and crusted snow cover in the immediate

FIGURE 3.4 Winter view looking west to Silverheels Mountain just north of Fairplay. The alpine zone above the treeline has large windblown areas that support fell field vegetation and snowbeds. In the foreground the snowpack is light, with a snow accumulation area on the lee side of the fence in the middle distance and a thin and crusted snow cover in the immediate unglaciated mountain regions probably provided important refugia for mountain plants.

The eastern floor of South Park is an arid plain that grades into the foothills of the Tarryall Mountains and the Pikes Peak massif. Pikes Peak is the best-known mountain in the Western Hemisphere and for many nineteenth-century travelers it "had the face of an old friend" (Fremont, 1887:405). In 1806 Zebulon Pike described this granite mountain as "un-climbable," misestimating its elevation at 5651 m—more than 1200 m more than its actual elevation. The first known successful ascent of the peak was accomplished by three members of the Long Expedition to the Rocky Mountains on July 14, 1820, led by the expedition's botanist and historian, Edwin James. It was James who set down the first observations and written impressions of Rocky Mountain alpine tundra plants, animals, and landscapes (James, 1825; Evans, 1997).

South Park's floor attains its highest elevation in the north, and its elevation decreases gradually to the south. From the town ofJefferson, at 2895 m elevation, to the town of Hartsel, at approximately 2700 m elevation, the park floor is a treeless plain, except on sedimentary and intrusive bedrock outcrops, which support forests of aspen, bristlecone pine, and other conifers. South of the Platte River's South Fork, the topography becomes rolling. Hills are forested on their tops, with steppe on slopes and flats. These hills merge into the Arkansas River Hills on the south and west.

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