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<br />OD1122 <br /> <br />-6- <br /> <br />The structures indicate that the Archaen ~ranites and schist <br />underlyin~ the lower valley are covered by the Jurassic sandstones. shales <br />and limestones. and above these lies a thiok deposit of Mancos Shale. Al- <br />though outoroppings are not general or numerous. the residual adobe soil <br />is ample evidenoe of the underlyin~ shale. Recent Quaternnry deposits <br />in the lovrer valley be~in southeast of Ridg;v.ay and consist of terraoe <br />gravels. till and glacial outwash. These are deposited on top of the <br />Mancos Shale. Along too flood-plain of the river and ita tributaries are <br />shallow alluvium deposits. <br /> <br />Of prinoipal importance in connection with the water use inves- <br />tigations is the faot that the study area is undl3rlain by the impervious <br />llsncos Shale. The oonclusion can be drawn that there is no deep peroola- <br />tion to other basins. It is also concluded that all water is forced to <br />the surfaoe and discharged in measurable streams. This conolusion is <br />reached beoause of the evidenoe of seepage lines above the shale in the <br />mesa bluffs along the Gunnison River and in the lov.er reaches of the Un- <br />compahgre River. and because of the shale bed of the river near its <br />mouth. <br />