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<br />f\\ <br />c. <br /> <br />~.: <br />I <br /> <br />GEOLOGY AND SOIl.S 1 <br /> <br />including anticlines, domes, and faults, <br />contribute to both the topographic relief and the <br />geohydrology of the region. <br /> <br />Several of the sedimentary formations in the <br />basin were deposited in marine or brackish <br />water environments. Occurrences of bedded and <br />disseminated sodium chloride (halite) and <br />calcium sulfate (gypsum) are observed, as are <br />clays with high contents of exchangeable sodium <br />and magnesium. <br /> <br />The soils of the Colorado River Basin closely <br />resemble the geologic formations from which <br />they were derived. Residual soils derived from <br />shale or sandstone are generally shallow. These <br />soils can contain appreciable soluble mineral <br />content due to residual and secondary mineral <br />formation from the parent material. Upon <br />weathering or irrigation, salts may accumulate <br />on or near the surface due to evaporation or <br />consumptive use by plants. <br />