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This book presents our knowledge about the nature and distribution of the soils of Arizona and their relation to the diversity of geology, climate, vegetation and fauna of the state. Many soil scientists and investigators in related fields have contributed to the fund of knowledge about Arizona soils in particular and soils in general. Plate 1, the Arizona General Soil Map, was prepared in cooperation with the Soil Conservation Service of the United States Department of Agriculture. * Much of the data used to compile the map were obtained by field soil scientists as part of the National Cooperative Soil Survey. Through basic research other scientists have extended knowledge about how soils formed and the basic properties of soils, which is invaluable in predicting and understanding the distribution of soils.

The nature and distribution of geology, physiography and climate are emphasized since they are important in affecting soil distribution. Vegetation distribution is addressed because of its relationship to the distribution of both climate and soils. Also, vegetation in turn may influence the nature of the soils. A chapter about animals and soils was not planned originally since the author has only limited knowledge and background in zoology and animal ecology. When Dr. Francis Hole of the University of Wisconsin reviewed the first draft of the manuscript he suggested that such a chapter would emphasize how animals might affect soil properties and how soil and vegetation create habitats for animals. Consequently, a chapter about animals and soil was written by Drs. Paul R. Krausman and R. William Mannan of the University of Arizona School of Renewable Natural Resources, with contributions from Dr. Hole. It is emphasized that the descriptions of the relationships between the geology, physiography, climate, vegetation and animals are keyed to the Arizona General Soil Map (Plate 1) and are, for the most part, generalized.

The mapping units of the Arizona General Soil Map (Plate 1) are named mostly by soil series, the lowest category of Soil Taxonomy, even though it would have been much more desirable and scientifically sound to have used the nomenclature of a higher category, such as the subgroup. Soil series were used as the main bases in developing the map because many potential users of the map might not be familiar with the Soil Taxonomy nomenclature of the higher categories and would be more comfortable with the more familiar soil series.

Soil series were used to describe some mapping units even though insufficient information or only preliminary data were available about the dominant soil series in the area. In several areas soil surveys have been completed and in others are nearing completion since the soil mapping units were developed and named. The more detailed information resulting from these recent soil surveys has revealed that soil series different from those used to describe some mapping units dominate. On the other hand, the soil series used to identify the mapping units of the Arizona General Soil Map (Plate 1) and the more recently

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recognized soil series are usually members of the same subgroup, hence the desirability of having used the higher category had it been possible.

The boundary between thermic and hyperthermic soils now is considered to be farther west in western Pima County than shown on the Arizona General Soil Map (Plate 1) and to extend somewhat into southern Maricopa County and southwestern Pinal County. This temperature boundary still is only approximate. It is anticipated that as additional knowledge about some Arizona soils is obtained that additional descriptive shifts will occur.

Dave Hendricks

April 1985


*. Copies of the original map from which Plate 1 was developed are available at no cost from the State Soil Scientist, 3008 Federal Building, 230 N. 1st Ave., Phoenix, Arizona 85025.

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