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<br />In the Upper Montane Zone. 1830 to 2440 m (6000 to 8000 ft). the <br />soils are shallow to moderately deep to a lithic. paralithic. or <br />weak duripan contact with sandy loam or gravelly sandy loam textures. <br />Those developing from volcanic materials are high in amorphous mate- <br />rials and vitric glass, and have thin, dark surface horizons and pale <br />to very pale brown subsoils. The amount of water held by the soils <br />available for plant use ranges from low to moderate. Most soils will <br />fall into one of the following Great Groups: Xerochrepts, Vi trandepts, <br />and Haplwnbrepts with frigid and mesic soil temperature regimes. <br /> <br />.. <br /> <br />In the Subalpine Zone, 2440 to 3050 m (8000 to 10 000 ft), the soils <br />are shallow to moderately deep. Those developing from volcanic mate- <br />rials are high in ,amorphous materials and vitric glass, and have dark <br />surface horizons and pale to very pale brown subsoils. The amotmt <br />of water held by the soils available for plant use is usually low. <br />Most soils will fall into one of the following Great Groups: <br />Xerumbrepts. Vitrandepts, and Xeropsamments with frigid soil temper- <br />ature regimes and possibly some cryic equivalents of these Great. <br />Groups. Within this zone are large expanses of bare 'rock outcrop. <br /> <br />SOIL MlISTURE <br /> <br />.. , <br /> <br />The moisture regime of the soils in the American River Basin is deter- <br />mined by geology; underlying rock or hardpan; site aspect; depth, slope <br /> <br />12 <br />