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2.06.8 ALLUVIAL VALLEY FLOOR DETERMINATION The entry to the proposed underground mine of Twin Pines No. 2 is located 2 1/2 miles southwest of Rockvale in Lewis Gulch, an emphemeral tributary to Oak Creek, which joins the Arkansas River near the town of Florence, Colorado. Lewis Gulch flows generally north and Oak Creek flows northeast, past the town of Rockvale which is 2 miles northeast of the mine site (fig. 2.04.5 - 1). South Oak Creek 1s a major tributary to Oak Creek. The confluence ie in Rockvale. Reconnaissance level alluvial valley floor investigations were carried out on Oak Creek, South Oak Creek, and Levis Gulch. Location and delineation of alluvial valley floor area ie shown on the General Mine Area drawing. The proposed mine entry in the NW 1/4 of the SW 1/4 of section 2, the T20S and R70W has been taken as the reference point from which adjacent areas are defined. Accordingly, a • two-mile radius of ground-water adjacent area would extend southeast of the proposed mine entry, while a two-mile radius of surface-water adjacent area would extend downstream along Oak Creek up to about the northern edge of section 36 (see drawing of General Mine Area). Lewis Gulch and South Oak Creek pass through section 2 which very likely would encompass moat of the permit area when the permit area boundary is finalized. 1.0 Oak Creek Oak Creek has its headwaters in the Wet Mountains (San Isabel National Forest). According to a report prepared for the City of Rockvale (Hydro Engineering, 1975), surface flow in Oak Creek ceases in the fall about 2 miles upstream of Rockvale. If this is true, Oak Creek is ephemeral. This diminuation of flow may be due to the extensive exploitation of the alluvial aquifer by the town of Rockvale for its municipal water supply. Flood irrigation has been historically practiced and is being practiced today along [he Oak Creek valley, at the western JFSA-70