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<br />r " <br /> <br />I <br />I I <br />I I <br />I <br />I <br />,I <br />II <br />i <br />11 <br />II <br />I <br />II <br />I <br />'"I <br />I <br />I <br />tl <br /> <br />'I <br />II <br /> <br />I <br />II <br />I, <br /> <br />'I <br /> <br />Z-j <br /> <br />The remainder of the Study Area can be topographically described as an <br />irregular open basin which is surrounded by high, steep to moderately steep <br />slopes. These slopes are as high as 1,100 feet. Well-developed drainage <br />courses descend into this basin from north, south, and west directions. A <br />mature floodplain of limited extent parallels the meandering course of South <br />St. Vrain Creek in the valley bottom. <br /> <br />Near the east boundary of the Study Area the valley markedly narrows. <br />This narrowing is represented by north-south trending hogback ridges which <br />reach' heights of 800 feet or more in the Study Area. <br /> <br />Beyond the eastern boundary of the Study Area the South St. Vrain Valley <br />rapidly widens to open meadows where the confluence of South St. Vrain Creek <br />and North St. Vrain Creek is located at the site of the City of Lyons. <br /> <br />2.3 Soil and Rock Outcrops <br /> <br />As illustrated on the Geologic Maps (Plates 1-8), soil deposits of <br />various types cover the bedrock at some locations. The character of these <br />deposits can be observed at some locations such as in roadway cut slopes and <br />in natural gullies. However, in most areas the soil is covered with a well- <br />developed topsoil mantle which precludes direct observation. <br /> <br />Many of the rock formations are covered with a thin (5 feet or less) <br />veneer of colluvial or residual soils. Because of thicker soil mantles and <br />more dense vegetat ive cover, rock format i onsare generally not well-exposed on <br />north-facing slopes. However, rock formations are often very well exposed on <br />slopes of other aspects and can be traced for thousands of feet in the field <br />and on aerial photographs. <br /> <br />2.4 Vegetation <br /> <br />The ground surface in much of the Study Area supports a sparse to <br />moderately dense growth of low grasses, scattered prickly pear cactus, and <br />chapparal. Limited stands of small Ponderosa pine can be found at lower <br />elevations on north-facing slopes. At higher elevations north-facing slopes <br />are often covered with dense stands of Douglas fir, Pcnderosa pine, and <br />aspen. Irrigated hay meadows and pasture lands occupy the lower flatter <br />slopes and the floodplain in the valley bottom. Cottonwoods and other <br />phreatic tress can be found in the valley bottom adjacent to the creek. <br /> <br />UEBLACKER ASSOCIATES, INCo <br />