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<br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br /> <br />GEOLOGY AND SOILS <br /> <br />Frijole Creek basin is in the southeast part of La Veta Syncline in <br /> <br /> <br />south-central Colorado. In this part of the state the regional dip of <br /> <br />the bedrock units is to the weat, into the deeper parts of the syncline. <br /> <br />Locally, the bedrock units can dip to the northwest and the southwest as <br /> <br /> <br />a result of local folding and faulting. The principal geologic units in <br /> <br /> <br />the area are sedimentary and include the Cretaceous Niobrara and Pierre <br /> <br /> <br />shales, the Tertiary Trinidad Sandstone, the Vermijo, Raton and Poison <br /> <br /> <br />Canyon formations, and basic lava flows. The lithology of these geo- <br /> <br /> <br />logic units includes shales, silt stones, sandstones and lava; most of <br /> <br /> <br />the basin is underlain by siltstones and shales. <br /> <br /> <br />Frijole Creek headwaters are near Fishers Peak on the northern part <br /> <br /> <br />of the Raton Mesa. The creek trends generally in a northeast direction <br /> <br /> <br />and flows across the sedimentary rocks. Lava flows, resistant to <br /> <br />erosion, cap the Raton Mesa. The Trinidad sandstone, a major landform <br /> <br /> <br />feature in the basin, forms the gently westward sloping sandstone ridge <br /> <br />near the center of the drainage basin. Other minor, unnamed, sandstones <br /> <br />also form ridges. <br /> <br /> <br />The sources of sediment transported by the flood are the fine- <br /> <br /> <br />grained sediments of the Cretaceous and Tertiary formations. Large <br /> <br />blocks of material moved by the flood were derived from competent <br /> <br /> <br />siltstones, sandstones and the lava flows. <br /> <br /> <br />In the upper reaches, geologic effects of the runoff were confined <br /> <br /> <br />largely to the zone of intense downpour. Localized sheet flooding on <br /> <br /> <br />hillslopes removed considerable soil material. Boulders and trees were <br /> <br /> <br />also transported down the slopes and were redeposited on the valley <br /> <br />floor. Channelized runoff scoured the streambed channel. <br /> <br />In the higher elevation areas of Frijole Creek the soils, as <br /> <br /> <br />classified by the U. S. Soil Conservation Service (SCS), are Capulin- <br /> <br /> <br />Vona Association, which are deep, well drained, gently sloping to <br /> <br /> <br />moderately steep soils on upland areas. Soils at the lower elevations, <br /> <br />which are predominant throughout the basin, are of the Gaynor-Samel-Linn <br /> <br /> <br />Associations, deep to shallow depths and well drained. <br /> <br />1II-4 <br />