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Alluvial fan <br />A low, outspread mass of loose materials and/or rock material, commonly with <br />gentle slopes. It is shaped like an open fan or a segment of a cone. The <br />material was deposited by a stream at the place where it issues from a narrow <br />mountain valley or upland valley or where a tributary stream is near or at its <br />junction with the main stream. The fan is steepest near its apex, which points <br />upstream, and slopes gently and convexly outward (downstream) with a gradual <br />decrease in gradient. <br />Alluvium <br />Unconsolidated material, such as gravel, sand, silt, clay, and various mixtures of <br />these, deposited on land by running water. <br />Alpha,alpha-dipyridyl <br />A compound that when dissolved in ammonium acetate is used to detect the <br />presence of reduced iron (Fe II) in the soil. A positive reaction implies reducing <br />conditions and the likely presence of redoximorphic features. <br />Animal unit month (AUM) <br />The amount of forage required by one mature cow of approximately 1,000 <br />pounds weight, with or without a calf, for 1 month. <br />Aquic conditions <br />Current soil wetness characterized by saturation, reduction, and redoximorphic <br />features. <br />Argillic horizon <br />A subsoil horizon characterized by an accumulation of illuvial clay. <br />Arroyo <br />The flat-floored channel of an ephemeral stream, commonly with very steep to <br />vertical banks cut in unconsolidated material. It is usually dry but can be <br />transformed into a temporary watercourse or short-lived torrent after heavy rain <br />within the watershed. <br />Aspect <br />The direction toward which a slope faces. Also called slope aspect. <br />Association, soil <br />A group of soils or miscellaneous areas geographically associated in a <br />characteristic repeating pattern and defined and delineated as a single map <br />unit. <br />Available water capacity (available moisture capacity) <br />The capacity of soils to hold water available for use by most plants. It is <br />commonly defined as the difference between the amount of soil water at field <br />moisture capacity and the amount at wilting point. It is commonly expressed as <br />inches of water per inch of soil. The capacity, in inches, in a 60-inch profile or to <br />a limiting layer is expressed as: <br />Custom Soil Resource Report <br />26 Index #10