UNIVERSITY OF CALIFORNIA 
 
 COLLEGE OF AGRICULTURE 
 
 AGRICULTURAL EXPERIMENT STATION 
 
 BERKELEY, CALIFORNIA 
 
 AN INDEX FOR RATING THE 
 
 AGRICULTURAL VALUE 
 
 OF SOILS 
 
 R. EARL STORIE 
 
 BULLETIN 556 
 SEPTEMBER, 1933 
 
 UNIVERSITY OF CALIFORNIA 
 BERKELEY, CALIFORNIA 
 
CONTENTS 
 
 PAGE 
 
 Introduction 3 
 
 Method of rating 5 
 
 Factor A: character of soil profile 5 
 
 Group I, unweathered or only slightly weathered secondary soils (recent 
 
 or young soils) 6 
 
 Group II, moderately weathered secondary soils (immature secondary soils) 13 
 Group III, strongly weathered secondary soils with dense clay subsoils 
 
 (semimature secondary soils) 14 
 
 Group IV, maturely weathered secondary soils with hardpan 15 
 
 Group V, strongly weathered soils with dense clay subsoils resting on con- 
 solidated materials 17 
 
 Group VI, soils developed on bedrock (primary or residual soils) ... 19 
 
 Factor B : texture of surface soil . • 21 
 
 Medium-textured soils 24 
 
 Medium-heavy-textured soils 25 
 
 Heavy-textured soils 25 
 
 Light-textured soils 26 
 
 Gravelly or cobbly soils 27 
 
 Stony soils 27 
 
 Factor C: soil-modifying conditions 28 
 
 Drainage 28 
 
 Alkali 28 
 
 Acidity 30 
 
 Infertility 30 
 
 Stratified subsoils (gravelly layers or stratified clay layers) 31 
 
 Shallow phases of alluvial soils 31 
 
 Eroded soils 31 
 
 Steep phases 32 
 
 Nonagricultural materials 32 
 
 Calculation of the index 34 
 
 Soil rating for a tract of land 35 
 
 Summary 39 
 
 Acknowledgments 39 
 
 List of selected references 40 
 
 Appendix: soil survey data in California 41 
 
AN INDEX FOR RATING THE AGRICULTURAL 
 VALUE OF SOILS 1 
 
 E. EARL STORIE 2 
 
 INTRODUCTION 
 
 The growth and production of plants is dependent very largely upon 
 the soil, and particularly the degree to which it presents conditions 
 favorable for the extension and development of plant roots. On soil that 
 is deep, pervious, relatively uniform in character, and that has fair 
 water-retaining capacity, a very wide range of plants may grow vigor- 
 ously. On soil with subsoil characteristics that retard the extension of 
 plant roots, growth and development of the plants may likewise be 
 retarded. If the subsoil is only moderately dense and root development 
 only slightly hindered, the growth and production may be good, but if 
 the density of the subsoil reaches that of a claypan, root penetration 
 may be decidedly limited, and if the subsoil is cemented into a true 
 hardpan, or underlaid by hard bedrock, penetration is definitely pre- 
 vented. 
 
 These variations in the character of the soil are directly related to its 
 origin, its mode of formation, and the age or stage of weathering. Recent 
 alluvial deposits are generally deep and pervious, and the profile, or 
 vertical section through the soil mass, shows no variations such as are 
 developed with age. Older soils, which have been exposed to the weather- 
 ing agents for very long periods of time, have subsoils that have become 
 more dense, until finally they may reach the claypan or hardpan stage. 
 Such soils, which are considered maturely weathered, have approached 
 a condition of equilibrium with the factors that have determined the 
 particular characteristics of their profiles. 
 
 The growth of plants on the soil is so closely related to these char- 
 acteristics of the profile, and the chemical composition of the several 
 horizons of the soil is likewise so closely related to the profile, that it 
 appears possible to rate the soils with the profile characteristics as a 
 base. 
 
 i Received for publication April 25, 1933. 
 
 2 Assistant Soil Technologist in the Experiment Station. 
 
 [3] 
 
4 University of California — Experiment Station 
 
 The index for rating soils as used herein is a numerical expression of 
 the degree to which a particular soil presents conditions favorable for 
 plant growth and crop production under good environmental condi- 
 tions. In arriving at the relative index of soils three general factors are 
 considered. These are (A) the character of the soil profile; (B) soil tex- 
 ture; and (C) other modifying factors, such as drainage, alkali, and 
 other miscellaneous conditions. Each of these three factors is evaluated 
 on the basis of 100 per cent for the most favorable or ideal condition, 
 with limiting maximum and minimum ratings ascribed to conditions 
 that are less favorable for plant growth. 
 
 The information set forth in the various soil-survey publications has 
 been used in developing the index. For a discussion of the soil survey 
 as a source of information, the reader is referred to the Appendix. In 
 studying, mapping, and classifying soils, the character and degree of 
 development of the soil profile, the reaction of the soil mass, the color, 
 the physical composition of the various horizons, the mode of formation 
 and composition of the parent material, the drainage and surface relief, 
 the alkali content, natural cover, etc., are considered in detail. 
 
 In arriving at the ratings the experience and judgment of the men 
 engaged in soil-survey work in California has been called upon, and the 
 ratings express the results of their collective studies of the relations of 
 these several conditions of the soil to the growth and production of 
 plants. Obviously, such ratings cannot be final and infallible and may 
 be changed as experience with the use of the soil index indicates. 
 
 The index is based on soil conditions alone independent of other 
 physical or economic factors which might determine the desirability of 
 growing certain plants in a given location ; hence it cannot be regarded 
 as by itself an index for land evaluation. In the latter, other factors, 
 such as variations in climate, availability of water for irrigation, facili- 
 ties for transportation and markets, social conditions, and the like, must 
 be included. 
 
 Although the soil is only one of the many factors that determine the 
 value of any given area of land surface, it is one that does not readily 
 change and that cannot be materially modified without the expenditure 
 of much effort. Its quality or value is one of the more stable elements 
 that determine land value, and an index for rating soils should serve to 
 simplify the work of land classification and evaluation. Other factors, 
 such as the climate, or the quality, quantity, and availability of water 
 for irrigation are likewise natural factors, more or less stable in char- 
 acter, that may be rated in a similar manner, but some physical, eco- 
 nomic, and social factors may be too variable or too readily changed to 
 permit of such treatment. Studies of these other factors that influence 
 
Bul. 556] Index for Rating Value of Soils 5 
 
 or modify land values may show the possibilities of developing indexes 
 for groups of these factors, and by integrating these several indexes, a 
 positive numerical expression of the relative value of any portion of the 
 land surface may result. 
 
 METHOD OF RATING 
 
 In most endeavors to rate soils on a comparative basis the "score card" 
 method has been used, and the rating determined by adding the points 
 credited to each of the soil characteristics or modifying factors. In the 
 index method here presented the rating is obtained by multiplying the 
 three factors, A times B times C, thus permitting any one of these to 
 dominate or control the final rating. As an example, a soil may have an 
 excellent profile condition warranting a rating of 100 per cent for factor 
 A, excellent surface-soil conditions giving 100 per cent for factor B, but 
 a bad alkali accumulation that would give a rating of 10 per cent for 
 factor C. Multiplying these three percentage ratings — A x B x C — gives 
 10 per cent as the index for this soil. The severe alkali accumulation 
 would dominate the quality of this soil, rendering it wholly unproduc- 
 tive for plants and would justify the index of 10 for that soil. On the 
 score-card basis, with possibly 20 or 25 points ascribed to alkali or simi- 
 lar conditions, its worst rating could be only 75 or 80. 
 
 The characteristics or conditions included under each of these factors 
 is described in the following chapter, and their bearing on the quality 
 of the soil is discussed. 
 
 FACTOR A : CHARACTER OF SOIL PROFILE 
 
 Factor A evaluates all the characteristics of the soil profile except the 
 texture of the surface soils. These characteristics, which are determined 
 by the kind of parent material, its mode of formation or accumulation, 
 and the age or degree of modification of the soil material by the weather- 
 ing agencies of climate, supplemented by vegetation and opposed by 
 erosion and deposition, serve to separate the soils into groups of related 
 individuals that are classed as soil series. 
 
 The suitability of soils for plant growth is dependent to a very large 
 extent on the profile characteristics that differentiate the soil series. A 
 series may be defined as "a group of soils having the same character of 
 profile ; that is, the same range in color, structure, and general sequence 
 of soil and subsoil horizons, the same general types of relief and drain- 
 age, and a common or similar origin and mode of formation." 3 The 
 
 3 Shaw, C. F. A glossary of soil terms. American Soil Survey Association Bul. 
 9:28-58. 1927. 
 
6 University of California — Experiment Station 
 
 name of the series implies all the characteristics used to define the soil 
 type except that of surface texture. 
 
 For factor A of this index, the soil series of California have been 
 placed in six general groups and a rating given soils of these groups. 
 In each group are series having similar modes of formation, similar 
 sequence of soil and subsoil horizons (i. e., layers), a comparable age, 
 and the same types of relief. The soil series of California officially rec- 
 ognized by the Bureau of Chemistry and Soils of the United States 
 Department of Agriculture and the California Agricultural Experi- 
 ment Station are listed alphabetically in table 1 with their position in 
 the six groups on the basis of factor A and with certain of their profile 
 characteristics indicated. 
 
 The profile characteristics and inclusive ratings for each group under 
 factor A are given in table 2. 
 
 Secondary 4 soils are placed in groups I, II, III, and IV; strongly 
 weathered secondary and primary 5 soils having dense clay subsoils de- 
 veloped on consolidated material in group V; and primary soils in 
 group VI. In the following sections characteristics of the soils in each 
 group are described and the profile rating of each explained. 
 
 Where soil surveys have been made, the necessary information for 
 this grouping can be obtained from the reports and maps, but if a survey 
 has not been made, then a field examination of the area to be rated is 
 needed in order to determine the profile characteristics. 
 
 GROUP I, UNWEATHERED OR ONLY SLIGHTLY WEATHERED 
 SECONDARY SOILS (RECENT OR YOUNG SOILS) 
 
 When they have been transported by water, the unweathered second- 
 ary soils are commonly referred to as the alluvial, stream-bottom, flood- 
 plain, alluvial-fan, or recent, transported soils. Group I also includes 
 soils deposited or reworked by the action of winds, commonly classed 
 as aeolian or wind-modified soils. 
 
 Soils of this group are characteristically more than 6 feet deep and 
 consist of a mass of soil material which has not been modified to any 
 extent by the action of weathering forces, which ultimately bring about 
 a change in the general character of the soil profile. It is because of this 
 that they are spoken of as unweathered soils, in contrast to the moder- 
 ately weathered soils of group II. 
 
 4 Secondary soils are those formed by the accumulation and weathering of 
 transported materials, originating from previously existing soils and from rock 
 debris, and are often referred to as alluvial, aeolian, or glacial soils, according to 
 the agency which transported them. 
 
 s Primary soils are those formed by the disintegration and decomposition of 
 rocks in place and the weathering of the resultant debris to true soil. 
 
Bul. 556] 
 
 Index for Rating Value of Soils 
 
 TABLE 1 
 
 Soil Series of California Listed Alphabetically Showing Their Positions in 
 
 the Six Groups on the Basis of Factor A, and also Showing the 
 
 Color* of the Surface Soil and the Soil Beaction 
 
 Series 
 
 Adelanto 
 
 Agate 
 
 Agueda 
 
 Aiken 
 
 Alamo 
 
 Aliso 
 
 Altamont 
 
 Alviso 
 
 Anderson 
 
 Anita 
 
 Antelope 
 
 Antioch 
 
 Arbuckle 
 
 Arnold 
 
 Arroyo Seco 
 
 Ataseadero 
 
 Ayar 
 
 Ballard 
 
 Barron 
 
 Bayside 
 
 Baywood 
 
 Bear 
 
 Belle vista 
 
 Bieber 
 
 Bishop 
 
 Botella 
 
 Bunting ville ... 
 
 Butte 
 
 Cachuma 
 
 Cajon 
 
 Canby 
 
 Capay 
 
 Carlsbad 
 
 Carrizo 
 
 Carson 
 
 Cayucos 
 
 Centerville 
 
 Chamise 
 
 Chino 
 
 Chualar 
 
 Churchill 
 
 Clear Lake 
 
 Climax 
 
 Coachella 
 
 Cole 
 
 Columbia 
 
 Commatti 
 
 Conejo 
 
 Contra Costa... 
 
 Group 
 
 Color of surface soil 
 
 Grayish brown 
 
 Brown 
 
 Dark brownish gray 
 
 Red 
 
 Dark gray 
 
 Reddish brown 
 
 Brown 
 
 Dark gray 
 
 Yellowish brown 
 
 Dark brown 
 
 Dark gray 
 
 Dark brown 
 
 Grayish brown 
 
 Brownish gray 
 
 Light brown 
 
 Dark brownish gray 
 
 Brown 
 
 Brown 
 
 Grayish brown 
 
 Grayish brown 
 
 Dark brown 
 
 Reddish brown 
 
 Light gray 
 
 Dark brown 
 
 Dark brownish gray 
 
 Dark brownish gray 
 
 Dark grayish brown 
 
 Brownish gray 
 
 Reddish brown 
 
 Light brownish gray 
 
 Light gray 
 
 Dark grayish brown 
 
 Brown 
 
 Light gray 
 
 Dark gray 
 
 Dark gray to black 
 
 Chocolate brown 
 
 Dark grayish brown 
 
 Dark gray 
 
 Dark brown 
 
 Grayish brown 
 
 Dark gray to black 
 
 Dark gray to black 
 
 Gray 
 
 Dark grayish brown 
 
 Light grayish brown 
 
 Gray 
 
 Dark gray to black 
 
 Reddish brown 
 
 General reaction 
 
 III 
 
 V 
 
 I 
 
 VI 
 
 IV 
 
 III 
 
 VI 
 
 I 
 
 I 
 
 II 
 
 V 
 
 III 
 
 I 
 
 VI 
 
 I 
 
 V 
 VI 
 
 II 
 
 II 
 
 I 
 
 I 
 
 I 
 
 IV 
 V 
 
 I 
 
 I 
 
 II 
 
 VI 
 
 III 
 
 I 
 
 V 
 
 III 
 
 VI 
 
 I 
 I 
 
 VI 
 
 III 
 
 V 
 
 II 
 II 
 
 IV 
 
 I 
 
 VI 
 
 I 
 
 II 
 I 
 
 II 
 I 
 
 VI 
 
 Calcareous subsoils 
 
 Calcareous substratum 
 
 Calcareous throughout 
 
 Moderately acid 
 
 Neutral 
 
 Calcareous subsoils 
 
 Calcareous subsoils 
 
 Usually saline 
 
 Neutral 
 
 Neutral 
 
 Neutral 
 
 Calcareous subsoils 
 
 Neutral 
 
 Moderately acid 
 
 Neutral 
 
 Slightly acid 
 
 Calcareous throughout 
 
 Neutral 
 
 Neutral 
 
 Moderately acid 
 
 Moderately acid 
 
 Neutral 
 
 Calcareous throughout 
 
 Neutral 
 
 Calcareous throughout 
 
 Neutral 
 
 Calcareous subsoils 
 
 Neutral 
 
 Neutral 
 
 Calcareous throughout 
 
 Calcareous subsoils 
 
 Calcareous subsoils 
 
 Slightly acid 
 
 Calcareous throughout 
 
 Calcareous subsoils 
 
 Moderately acid.. 
 
 Calcareous subsoils 
 
 Moderately acid 
 
 Calcareous subsoils 
 
 Neutral 
 
 Calcareous throughout 
 
 Calcareous subsoils 
 
 Neutral 
 
 Calcareous throughout 
 
 Slightly acid 
 
 Neutral 
 
 Calcareous subsoils 
 
 Neutral 
 
 Neutral 
 
 * Color, one of the most obvious of the many soil characteristics, is so closely correlated with the condi- 
 tions under which the soil has been formed that it often gives considerable information concerning the 
 other characteristics of the soil, such as the organic matter content. 
 
University of California — Experiment Station 
 
 TABLE 1— (Continued) 
 
 Series 
 
 Group 
 
 Color of surface soil 
 
 General reaction 
 
 Coquille 
 
 Corning 
 
 Corralitos 
 
 Cuyama 
 
 Danville 
 
 Daulton 
 
 Delaney 
 
 Delano 
 
 Delhi 
 
 Denverton 
 
 Diablo 
 
 Diamond Springs 
 
 Docas 
 
 Domino 
 
 Dublin 
 
 Ducor 
 
 Dunnigan 
 
 Egbert 
 
 Elder 
 
 Elkhorn 
 
 Elna 
 
 Empire 
 
 Encina 
 
 Escondido 
 
 Esparto 
 
 Exeter 
 
 Fallbrook 
 
 Fancher 
 
 Farwell 
 
 Feather 
 
 Ferndale 
 
 Foster 
 
 Fresno 
 
 Fullerton 
 
 Galveston 
 
 Gleason 
 
 Garey 
 
 Gazelle 
 
 Gila 
 
 Gloria 
 
 Goldridge 
 
 Gould 
 
 Greenfield 
 
 Gridley 
 
 Hames 
 
 Hanford 
 
 Hartley 
 
 Hesperia 
 
 Holccmb 
 
 Holland 
 
 Holtville 
 
 Honcut 
 
 Hovey 
 
 Huerhuero 
 
 Hugo 
 
 Imperial 
 
 Indio 
 
 I 
 
 III 
 
 II 
 
 II 
 
 I 
 VI 
 
 I 
 II 
 
 I 
 III 
 VI 
 VI 
 
 II 
 
 IV 
 
 I 
 
 II 
 
 III 
 
 I 
 
 I 
 
 II 
 
 IV 
 
 III 
 
 VI 
 VI 
 
 II 
 III 
 
 VI 
 IV 
 
 I 
 I 
 I 
 I 
 rv 
 ii 
 i 
 
 VI 
 
 ii 
 
 IV 
 
 i 
 
 IV 
 
 VI 
 
 V 
 
 I 
 III 
 III 
 
 I 
 III 
 
 I 
 III 
 
 VI 
 
 I 
 
 I 
 
 II 
 III 
 
 VI 
 
 I 
 I 
 
 Grayish brown, mottled.. 
 
 Light red 
 
 Brown 
 
 Brownish gray 
 
 Dark brown 
 
 Reddish brown 
 
 Light brownish gray 
 
 Light reddish brown 
 
 Light brown 
 
 Dark brown 
 
 Dark gray to black 
 
 Grayish yellow 
 
 Brownish gray 
 
 Light brownish gray 
 
 Dark gray to black 
 
 Dark chocolate brown 
 
 Brownish gray 
 
 Dark gray 
 
 Dark brownish gray 
 
 Brown 
 
 Light gray 
 
 Reddish brown 
 
 Dark brown 
 
 Yellowish brown 
 
 Light brown 
 
 Reddish brown 
 
 Reddish brown 
 
 Reddish brown 
 
 Light chocolate brown 
 
 Brown 
 
 Brownish gray 
 
 Dark brownish gray 
 
 Brownish gray 
 
 Brown 
 
 Dark gray 
 
 Dark brown '. 
 
 Light reddish brown 
 
 Dark brownish gray 
 
 Light purplish brown 
 
 Brownish red 
 
 Yellowish gray 
 
 Reddish brown 
 
 Brown 
 
 Brown 
 
 Brown 
 
 Light brown 
 
 Light brownish red 
 
 Light brown 
 
 Light brown 
 
 Brown 
 
 Light purplish gray 
 
 Reddish brown 
 
 Dark gray to black 
 
 Light grayish brown 
 
 Yellowish brown 
 
 Light purplish gray 
 
 Brownish gray 
 
 Acid; saline 
 
 Neutral 
 
 Slightly acid 
 
 Calcareous throughout 
 
 Neutral 
 
 Neutral 
 
 Neutral 
 
 Calcareous subsoils 
 
 Neutral 
 
 Calcareous subsoils 
 
 Calcareous subsoils 
 
 Slightly acid 
 
 Calcareous throughout 
 
 Calcareous throughout 
 
 Neutral 
 
 Calcareous subsoils 
 
 Calcareous subsoils 
 
 Moderately acid 
 
 Calcareous subsoils 
 
 Slightly acid 
 
 Calcareous throughout 
 
 Strongly acid 
 
 Slightly acid 
 
 Neutral 
 
 Slightly acid 
 
 Neutral 
 
 Neutral 
 
 Neutral 
 
 Calcareous subsoils 
 
 Neutral 
 
 Moderately acid 
 
 Calcareous throughout 
 
 Calcareous; alkaline 
 
 Neutral 
 
 Usually saline 
 
 Neutral 
 
 Moderately acid 
 
 Calcareous throughout 
 
 Calcareous throughout 
 
 Neutral 
 
 Moderately acid 
 
 Neutral 
 
 Neutral 
 
 Neutral 
 
 Slightly acid 
 
 Neutral 
 
 Neutral 
 
 Calcareous subsoils 
 
 Moderately acid 
 
 Slightly acid 
 
 Calcareous throughout 
 
 Neutral 
 
 Calcareous subsoils 
 
 Calcareous subsoils 
 
 Moderately acid 
 
 Calcareous, alkaline 
 
 Calcareous throughout 
 
Bul. 556 
 
 Index for Rating Value of Soils 
 
 TABLE 1— (Continued) 
 
 Series 
 
 Group 
 
 Color of surface soil 
 
 General reaction 
 
 Johnsonville 
 
 Reefers 
 
 Rettleman 
 
 Rimball 
 
 Rirkwood 
 
 Rlamath 
 
 Rneeland 
 
 Ronokti 
 
 Laguna 
 
 Lahontan 
 
 Landlow 
 
 Las Flores 
 
 Las Posas 
 
 Lewis 
 
 Lindsey 
 
 Linne 
 
 Liver more 
 
 Lockwood 
 
 Los Angeles 
 
 Los Osos 
 
 Lynndyl 
 
 Madera 
 
 Manzanita . . 
 
 Marcuse 
 
 Maricopa 
 
 Marina 
 
 Mariposa 
 
 Marvin 
 
 Marys ville . . 
 
 May wood 
 
 McClusky 
 
 Media 
 
 Melbourne . 
 
 Meloland 
 
 Merced 
 
 Merriam 
 
 Metz 
 
 Mocho 
 
 Modoc 
 
 Mojave 
 
 Mono 
 
 Monserate. .. 
 
 Montague 
 
 Monterey 
 
 Montezuma 
 
 Moro Cojo 
 
 Nacimiento 
 
 Niland 
 
 Nord 
 
 Norman 
 
 Oakdale 
 
 Oakley 
 
 Ojai 
 
 Olcott 
 
 Olivenhain.... 
 Olympic 
 
 II 
 III 
 VI 
 III 
 III 
 III 
 
 V 
 VI 
 
 I 
 
 II 
 
 V 
 
 V 
 
 VI 
 
 VI 
 
 III 
 II 
 
 VI 
 
 II 
 III 
 
 VI 
 VI 
 
 II 
 
 IV 
 
 III 
 
 III 
 
 II 
 
 I 
 
 VI 
 
 II 
 
 IV 
 
 I 
 III 
 
 VI 
 VI 
 
 I 
 
 III 
 
 III 
 
 I 
 
 I 
 
 II 
 III 
 
 IV 
 V 
 
 rv 
 
 VI 
 
 in 
 
 VI 
 VI 
 
 II 
 
 I 
 
 III 
 
 I 
 
 I 
 
 III 
 
 III 
 
 V 
 VI 
 
 Brown 
 
 Brownish red 
 
 Gray 
 
 Brownish red 
 
 Dark gray 
 
 Dark gray 
 
 Dark grayish brown 
 
 Brown 
 
 Light brownish gray ... 
 
 Light gray 
 
 Brown to dark brown 
 
 Light gray 
 
 Brownish red 
 
 Dark brown 
 
 Brownish gray.... 
 
 Dark gray 
 
 Dark brownish gray 
 
 Dark grayish brown 
 
 Grayish brown 
 
 Light brown 
 
 Dark brown 
 
 Light grayish brown... 
 
 Brown 
 
 Brownish red 
 
 Dark gray 
 
 Reddish brown 
 
 Brown 
 
 Brownish yellow 
 
 Light brown 
 
 Reddish brown 
 
 Yellowish brown 
 
 Dark grayish brown 
 
 Brown 
 
 Brown 
 
 Light brownish gray.... 
 
 Dark gray to black 
 
 Light reddish brown. . 
 
 Light brown 
 
 Brown 
 
 Dark brown 
 
 Reddish brown 
 
 Light brownish gray... 
 
 Brown 
 
 Dark grayish brown 
 
 Reddish brown 
 
 Dark gray to black 
 
 Reddish brown 
 
 Brownish gray 
 
 Light brownish gray... 
 
 Grayish brown 
 
 Dark brown 
 
 Grayish brown 
 
 Light brown 
 
 Pale yellow 
 
 Brown 
 
 Light brown 
 
 Dark brown 
 
 Calcareous subsoils 
 
 Slightly acid 
 
 Calcareous throughout 
 
 Neutral 
 
 Neutral 
 
 Neutral 
 
 Moderately acid 
 
 Slightly acid 
 
 Neutral 
 
 Calcareous; alkaline 
 
 Calcareous subsoils 
 
 Slightly acid 
 
 Neutral 
 
 Calcareous subsoils 
 
 Usually alkaline 
 
 Calcareous subsoils 
 
 Calcareous throughout 
 
 Neutral 
 
 Neutral 
 
 Calcareous subsoils 
 
 Moderately acid 
 
 Calcareous throughout 
 
 Neutral 
 
 Moderately acid 
 
 Usually alkaline 
 
 Neutral 
 
 Slightly acid 
 
 Moderately acid 
 
 Calcareous subsoils 
 
 Neutral 
 
 Neutral 
 
 Moderately acid 
 
 Neutral 
 
 Moderately acid 
 
 Calcareous throughout 
 
 Calcareous subsoils 
 
 Calcareous subsoils 
 
 Calcareous throughout 
 
 Calcareous throughout 
 
 Neutral 
 
 Calcareous throughout 
 
 Calcareous throughout 
 
 Calcareous subsoils 
 
 Calcareous subsoils 
 
 Moderately acid 
 
 Calcareous subsoils 
 
 Moderately acid 
 
 Calcareous throughout 
 
 Calcareous; alkaline 
 
 Calcareous throughout 
 
 Often alkaline 
 
 Neutral 
 
 Slightly acid 
 
 Neutral 
 
 Neutral 
 
 Slightly acid 
 
 Moderately acid 
 
10 
 
 University of California — Experiment Station 
 
 TABLE 1— (Continued) 
 
 Series 
 
 Orland 
 
 Oxnard 
 
 Pajaro 
 
 Panoche 
 
 Pentz 
 
 Pinole 
 
 Pit 
 
 Placentia 
 
 Pleasanton 
 
 Pond 
 
 Poplar 
 
 Porterville 
 
 Preston 
 
 Ramada 
 
 Ramona 
 
 Redding 
 
 Rhonerville 
 
 Rincon 
 
 Rocklyn 
 
 Rosamond 
 
 Rositas 
 
 Sacramento 
 
 Salinas 
 
 Salsipuedes 
 
 San Gabriel 
 
 San Joaquin 
 
 San Marcos 
 
 San Ysidro 
 
 Santa Cruz 
 
 Santa Lucia 
 
 Santa Rita 
 
 Santa Ynez 
 
 Santiago 
 
 Shasta 
 
 Shedd 
 
 Sheridan 
 
 Sierra 
 
 Siskiyou 
 
 Sites 
 
 Solano 
 
 Soledad 
 
 Sorrento 
 
 Stacy 
 
 Standish 
 
 Stockpen 
 
 Stockton 
 
 Sunol 
 
 Sunrise 
 
 Superstition 
 
 Surprise 
 
 Sutter 
 
 Tangair 
 
 Tassajero 
 
 Tehama 
 
 Tierra 
 
 Tijeras 
 
 Tujunga 
 
 Group 
 
 II 
 
 I 
 
 I 
 
 I 
 
 VI 
 
 III 
 
 I 
 
 III 
 
 II 
 
 II 
 
 II 
 
 II 
 
 I 
 
 I 
 
 II 
 IV 
 
 II 
 II 
 
 IV 
 
 II 
 I 
 
 II 
 
 II 
 
 II 
 
 I 
 
 IV 
 
 II 
 II 
 
 VI 
 VI 
 
 II 
 
 III 
 
 II 
 
 II 
 
 VI 
 VI 
 VI 
 VI 
 VI 
 
 III 
 II 
 I 
 
 I 
 
 V 
 
 III 
 
 V 
 
 II 
 
 IV 
 
 I 
 I 
 I 
 
 IV 
 
 I 
 II 
 
 V 
 V 
 
 I 
 
 Color of surface soil 
 
 Light grayish brown 
 
 Brown 
 
 Brown 
 
 Brownish gray 
 
 Dark grayish brown 
 
 Yellowish brown 
 
 Dark gray to black 
 
 Brownish red 
 
 Brown 
 
 Brownish gray 
 
 Light brown 
 
 Chocolate brown 
 
 Light grayish brown 
 
 Light yellowish brown 
 
 Reddish brown 
 
 Brownish red 
 
 Dark brownish gray 
 
 Brown 
 
 Brownish red 
 
 Light grayish brown 
 
 Light brownish gray 
 
 Dark gray to black 
 
 Dark brownish gray 
 
 Dark brown 
 
 Light brown 
 
 Brownish red 
 
 Dark brownish gray 
 
 Brownish gray 
 
 Reddish brown 
 
 Dark grayish brown 
 
 Grayish brown 
 
 Dark grayish brown 
 
 Dark gray 
 
 Light brownish gray 
 
 Gray 
 
 Dark gray 
 
 Brownish red 
 
 Brownish gray 
 
 Brownish red 
 
 Dark brownish gray 
 
 Brown 
 
 Light brown 
 
 Light brown 
 
 Grayish brown 
 
 Light gray 
 
 Dark gray to black 
 
 Reddish brown 
 
 Light reddish brown 
 
 Gray 
 
 Dark brown 
 
 Light brownish gray 
 
 Brownish gray 
 
 Brown 
 
 Light yellowish brown 
 
 Dark grayish brown 
 
 Light reddish brown 
 
 Light brownish gray 
 
 General reaction 
 
 Neutral 
 
 Calcareous subsoils 
 
 Neutral 
 
 Calcareous throughout 
 
 Neutral 
 
 Neutral 
 
 Neutral 
 
 Neutral 
 
 Neutral 
 
 Calcareous; alkaline 
 
 Neutral 
 
 Calcareous subsoils 
 
 Slightly calcareous 
 
 Neutral 
 
 Neutral 
 
 Strongly acid 
 
 Strongly acid 
 
 Neutral 
 
 Slightly acid 
 
 Calcareous throughout 
 
 Calcareous throughout 
 
 Slightly calcareous subsoils 
 
 Calcareous subsoils 
 
 Slightly acid 
 
 Neutral 
 
 Slightly acid 
 
 Calcareous subsoils 
 
 Neutral 
 
 Moderately acid 
 
 Neutral 
 
 Calcareous throughout 
 
 Neutral 
 
 Calcareous subsoils 
 
 Neutral 
 
 Calcareous throughout 
 
 Neutral 
 
 Moderately acid 
 
 Neutral 
 
 Moderately acid 
 
 Calcareous subsoils 
 
 Neutral 
 
 Calcareous subsoils 
 
 Calcareous throughout 
 
 Calcareous throughout 
 
 Calcareous subsoils 
 
 Calcareous subsoils 
 
 Neutral 
 
 Calcareous throughout 
 
 Calcareous throughout 
 
 Neutral 
 
 Neutral 
 
 Moderately acid 
 
 Neutral 
 
 Neutral 
 
 Moderately acid 
 
 Calcareous throughout 
 
 Neutral 
 
Bul. 556] 
 
 Index for Rating Value of Soils 
 
 11 
 
 TABLE 1— (Concluded) 
 
 Series 
 
 Group 
 
 Color of surface soil 
 
 General reaction 
 
 Tulare 
 
 II 
 
 V 
 
 V 
 
 VI 
 
 VI 
 
 I 
 
 VI 
 
 I 
 
 VI 
 
 II 
 
 VI 
 
 II 
 
 I 
 
 I 
 
 II 
 
 I 
 
 VI 
 VI 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 Vista 
 
 
 
 
 
 Strongly acid 
 
 
 
 
 Dark brownish gray 
 
 
 
 
 wants 
 
 
 
 
 
 
 
 
 
 
 
 
 Yolo 
 
 
 
 
 
 
 
 Dark gray to black 
 
 
 
 
 TABLE 2 
 Eating of Soils on the Basis of Profile Characteristics 
 
 Group 
 
 Group 
 number 
 
 Description 
 
 Surface relief 
 
 Profile rating 
 (factor A) 
 in per cent 
 
 Unweathered or slightly 
 weathered secondary 
 
 I 
 
 Loose and friable material 
 6 feet or more deep 
 
 Flat or gently slop- 
 ing 
 
 95-100 
 
 Moderately weathered sec- 
 ondary soils 
 
 II 
 
 Deep but have compact sub- 
 soils and slight to moderate 
 accumulation of clay 
 
 Terraces, benches 
 or valley floors 
 
 80-95 
 
 Strongly weathered sec- 
 ondary soils 
 
 III 
 
 Dense clay subsoils, loose un- 
 consolidated parent mate- 
 rial 
 
 Terraces 
 
 40-80 
 
 Maturely weathered sec- 
 ondary soils 
 
 IV 
 
 Hardpan soils, often have 
 fairly dense clay subsoils 
 
 Flat terraces, valley 
 floors, often hog- 
 wallow surface 
 
 5-60 
 
 Strongly weathered soils 
 having dense clay sub- 
 soils, developed on con- 
 solidated material 
 
 V 
 
 Coastal plain soils 
 
 High eroded ter- 
 races 
 
 20-40 
 
 Primary soils (residual) 
 
 VI 
 
 Formed in place from decom- 
 position and disintegration 
 of underlying bedrock 
 
 Hilly, rolling or 
 mountainous 
 
 20-70 
 
12 
 
 University of California — Experiment Station 
 
 The most valuable agricultural soils of California fall in this group ; 
 they occur on the flood plains and alluvial fans of many of the California 
 streams. They are especially valuable for orchards, vegetables, and deep- 
 rooted field crops. Yields on many of the medium-textured alluvial soils 
 have remained consistently high for a long period without recourse to 
 fertilization. The crop yields are consistently higher than on soils of the 
 other groups. These soils, providing conditions favorable for the growth 
 of almost any crop plants, have been given a factor-A rating of 95 to 
 100 per cent. 
 
 TYPE }^^ -^^-^-^^tX C^^^y LOCATION _ £? l *_"7~~*: ^^^^^HL^i^f^.^t^Z. 
 
 relief _ BPh^J^l _ elevation § -4^L drainage _>y>i£_ hyo^X, 
 
 RAINFALL _ 18. i?«J*^L NATIVE VE6ETATI0N _ Q^-^a^^O- _ _ USE _ 'M r '=d^.' u £^. _ _ 
 ORIGIN ^f^^^jk^^r^^ DEVELOPMENT Or PROFILE _ 1&-S*"*- jf»*£-^_ _ _ _ _ 
 
 REMARKS 
 
 
 
 
 
 
 f~rt-o-l£-C< /coJTj^va fZ 
 
 ItrO . 
 
 
 
 PROFILE 
 
 COLOR 
 
 TEXTURE 
 
 STRUCTURE 
 
 CONSISTENCE 
 
 AND 
 
 DENSITY 
 
 REACTION 
 
 MISCELLANEOUS 
 
 ROOTS, STONES, CONCRETIONS, 
 PERMEABILITY, ETC. 
 
 -. 
 
 
 
 *?Z$ 
 
 <XH.VrTuuJLaJl~- 
 
 
 n.o 
 
 
 
 
 12- 
 24- 
 
 
 
 
 £J± 
 
 
 &Jlu(&KtJU44_ 
 
 ^.Jk 
 
 7.o 
 
 -*V /uxrU. <x»JL 
 
 36- 
 
 
 
 
 
 
 
 
 48- 
 
 
 
 
 
 
 
 
 60- 
 
 
 
 
 
 
 
 
 Fig. 1. — Soil description and profile of Yolo fine sandy loam. This type of form is 
 of use in reporting and showing tire characteristics of a soil by horizons. 
 
 Variation in texture of the surface soils is rated under factor B and 
 discussed in a separate section. Any conditions unfavorable to plant 
 growth, such as gravelly subsoil layers, injurious amounts of alkali, 
 high acidity, or poor drainage conditions that may occur are rated under 
 factor C. 
 
 The Hanford, Yolo, Columbia, and Honcut are extensively developed 
 soil series of this group. The fact that some of the best crop yields of the 
 state are secured on these soils indicates the soundness of the high rating 
 given them. Figure 1 gives a typical profile of a Yolo fine sandy loam 
 which serves to illustrate the general depth and pervious nature of the 
 profiles of soils in group I. 
 
Bul. 556] 
 
 Index for Rating Value of Soils 
 
 13 
 
 GROUP II, MODERATELY WEATHERED SECONDARY SOILS 
 (IMMATURE SECONDARY SOILS) 
 
 Group II consists of water-laid or wind-laid deposits which have been 
 subjected to weathering for a sufficient period to develop subsoil char- 
 acteristics very distinct from those of the recent or un weathered group. 
 These have profiles with clearly evident clay accumulations in the mod- 
 erately compact subsoil layers, while many of the soils also have accum- 
 ulations of lime in the subsoil. Subsoils are permeable to moisture and 
 roots, although not to the same degree as the younger soils of group I. 
 
 TYPE JT^asr*-™^ ^a^JLi Z»yy*^± _ LOCATION _££ ^^S^^Y^P^t-— dQ^^tJQ^g' £**r$H_. 
 
 RELIEF ^^2^^*>t«ee. ELEVATION J^J^jjffti _ DRAINAGE _ J^>j43 4 nj ^A: 
 
 RAINFALL JZ. «2»?*«± NATIVE VE6ETAT10N _Q^a^>~_- J>"±f^L_ USE _WjM~J^3- 1 
 
 ORIGIN'S*"*^!*^ -| ,% ^ > rir g^^ife DEVELOPMENT OF PROFILE J=*T^ i? M 5i-'~l. ^^t^*X^_ 
 
 REMARKS U^Cj^u^o _a. 
 
 p.a&*^_ f) 9Q. _ 
 
 STRUCTURE 
 
 CONSISTENCE 
 
 AND 
 
 DENSITY 
 
 MISCELLANEOUS 
 ROOTS, STONES, CONCRETIONS, 
 PCRMEABIMTY, ETC. 
 
 "EL 
 
 "t«^wJ,*L^ 
 
 
 -rvu&ltJL 
 
 f^Lh^JL^Mx. 
 
 
 TfH 
 
 JLfrOJtrKS 
 
 a^Loyr^iiiaH, 
 
 
 
 
 n.o 
 
 »»*>i-»~L-e<-£C«_ 
 
 
 7.6 - 73 
 
 ■+, J 
 
 /C0tV»*v 
 
 yofVOKt 
 
 ***f 
 
 7.0 
 
 Fig. 2. — Profile description of Eamona sandy loam, San Diego County, California, 
 illustrative of the general characteristics of the soils in group II (moderately weath- 
 ered secondary soils), having compact subsoil layers with clay accumulations. 
 
 This is evidenced by the somewhat slower penetration of irrigation 
 water. The parent material below the subsoil is usually permeable to a 
 depth of 6 feet or more. These soils usually occur on smooth terraces 
 and mesas, lower benches, and in some cases on typical alluvial-fan sur- 
 faces, usually being slightly higher in elevation than those of group I. 
 Many of the soil series in this group occur on terraces which have been 
 slightly eroded so that the topography is somewhat irregular, especially 
 on the borders. 
 
 These are good soils, although of less value than those of group I, since 
 they are older, have a moderate subsoil compaction and accumulation 
 of clay, which retards the penetration of moisture, and may have a more 
 
14 
 
 University of California — Experiment Station 
 
 irregular surface, which lessens their value for irrigated crops. They 
 are given a factor- A rating of 80-95 per cent. 
 
 Soils of the Ramona series are the best known in this group. A typical 
 profile description of Ramona sandy loam is given in figure 2. 
 
 GROUP III, STRONGLY WEATHERED SECONDARY SOILS WITH 
 DENSE CLAY SUBSOILS (SEMIMATURE SECONDARY SOILS) 
 
 The soils of group III are characterized by a very heavy, dense, plastic 
 clay subsoil layer that breaks up when dry into very hard dense struc- 
 tural aggregates. These are semimaturely weathered soils. They are of 
 
 TYPE Jhy^L t> -^--4^L ■<**2fpi &*?"?— LOCATION _ Qs*^£u^^_y^<r^«^^L _Ht"<=?yL' 
 
 RELIEF. fX^L'^^P 2 -— ELEVATION _ _ _4P^^ DRAINAGE ^^J^y^±^. 
 
 RAINFALL J8. hr^^L. _ NATIVE VE6ETATI0N _<3/c^O^<. _ _ USE ~Eo^aa. 
 
 ORIGIN _ J^kpd 2"-*X*iV-*L DEVELOPMENT OF PROFILE _ ^y^s^&& . 
 
 REMARKS _ _— _ _ — — ■ 
 
 Th&UL. Ka&y±g. _jrP—<S>Cl 
 
 COLOR 
 
 STRUCTURE 
 
 CONSISTENCE 
 
 AND 
 
 DENSITY 
 
 MISCELLANEOUS 
 ROOTS, STONES, CONCRETIONS, 
 PERMEABILITY, ETC. 
 
 JLbrxsm, 
 
 *¥4 
 
 
 except 
 
 
 ianyhj LcrtMy 
 
 &v*ch OAAM^Jl 
 
 jLytrZA. 
 
 
 
 ^RJs 
 
 Orr&.icf' 
 
 
 eM^&J 
 
 /V^> 
 
 
 ^-f' 
 
 
 
 JLo-a^r^/ 
 
 JUlLj 
 
 d-oSAJU* 
 
 Jt 
 
 
 Fig. 3. — Profile description of Antioeh fine sandy loam from Solano County, Cali- 
 fornia; claypan soil of group III. 
 
 alluvial or marine origin, but have been materially changed in chemical 
 and physical make-up since they were deposited. All have a leached 
 surface usually of sandy texture, low in available plant food, and nor- 
 mally moderately acid in reaction. There is usually an abrupt change 
 from the sandier surface layers to the heavy, dense clay subsoils. The 
 downward movement of water is markedly retarded and the soils be- 
 come temporarily water-logged after heavy rains. The heavy subsoils 
 are underlaid by pervious parent materials penetrable by roots and 
 water. In some cases these parent materials are loose soil, while in others 
 they are fairly compact, but in all cases they are penetrable to a depth 
 of 6 feet or more. 
 
Bul. 55(5 J 
 
 Index for Rating Value of Soils 
 
 15 
 
 These soils occupy terraces or benches which are often somewhat 
 eroded. They are of common occurrence in most of the California valleys 
 and along the coast line of central and southern California. 
 
 Their value is limited by the heavy subsoil layer and often to some 
 extent by the eroded surface, which makes them difficult to irrigate and 
 cultivate. They are given a rating of 40-80 per cent. Within these limits 
 the rating will depend on the depth to the clay layer and the general 
 surface conditions. Soils occurring under higher rainfall, such as the 
 
 Fig. 4. — Profile of San Joaquin sandy loam (hardpan soil, group IV), San Joaquin 
 Valley, California. The hardpan layer is about 2 feet thick, with about 3 feet of soil 
 material overlying the hardpan. (Photograph by C. F. Shaw.) 
 
 Antioch series, have surface soils as much as 20 to 24 inches in thickness, 
 while the southern California soils of similar character (such as the 
 Huerhuero series), but located where the rainfall is much less, have 
 much shallower surface soils. Figure 3 gives details of a profile of the 
 Antioch fine sandy loam located near Fairfield. This soil is given a 
 higher rating than the Huerhuero because of its depth of surface soil 
 and the level surface of the terrace on which it occurs. 
 
 GROUP IV, MATURELY WEATHERED SECONDARY SOILS 
 WITH HARDPAN 
 
 The soils with hardpan appear to have reached a mature age or stage 
 of weathering, and are characterized by the cemented, rock-like subsoil 
 horizon (fig. 4) that has been formed as a direct result of the soil- 
 weathering process. True hardpans do not soften when saturated with 
 
16 
 
 University of California — Experiment Station 
 
 water, thus being distinguished from certain dense clay subsoils, which 
 are often erroneously referred to as hardpan layers. 
 
 True hardpan soils occur under arid or semiarid climatic conditions, 
 and the depth to the hardpan layer is usually closely correlated with 
 the depth of the annual penetration of rainfall. A dense clay layer nor- 
 mally lies just above the hardpan. Where the hardpan is continuous and 
 unbroken, drainage conditions are poor and the surface soil becomes 
 saturated after heavy rains. They usually occur on sloping terraces or on 
 valley floors and often have a "hogwallow" surface of small mounds and 
 depressions (fig. 5). Some areas have suffered considerable erosion. 
 
 Fig. 5. — Natural mounds or "hogwallow" surface of San Joaquin sandy loam, 
 Kern County, California. (Photograph by C. F. Shaw.) 
 
 The largest areas of hardpan soils lie in the Great Valley of Califor- 
 nia, especially in the San Joaquin. They are also scattered throughout 
 the valleys of southern California. They occupy a total of over three 
 million acres in the state-. 
 
 Considerable discussion has developed over the subject of the utiliza- 
 tion of hardpan soils and the extent to which the undesirable features, 
 such as the limited depth of the soil material overlying the hardpan and 
 the thickness and hardness of the hardpan, may reduce the value of such 
 soils. The rooting zone of plants is limited when the hardpan is close to 
 the surface. The moisture capacity is limited by the shallow depth of 
 soil above the hardpan; irrigation water must be applied frequently 
 and in small amounts, or saturation and poor drainage will result ; and 
 other difficulties arise owing to the limited mass of soil material. The 
 organic content of hardpan soils is usually low, and the clay fractions of 
 such character that the soils have a tendency to bake hard on drying, 
 thus rendering them more difficult to handle. The undulating hogwal- 
 low surface configuration of such lands also renders them difficult to 
 
Bul. 556] 
 
 Index for Rating Value of Soils 
 
 17 
 
 prepare for irrigation. When they are leveled, it is noted that crops re- 
 spond better in the filled places than they do on the areas where soil has 
 been removed. 
 
 The following ratings are based on the depth to hardpan : 
 
 Rating, in 
 per cent 
 Hardpan less than 1 foot 5-10 
 
 1 to 2 feet 10-20 
 
 2 to 3 feet 20-30 
 
 3 to 4 feet 30-40 
 
 4 to 6 feet 40-60 
 
 These figures should be raised in certain instances where the hardpan is 
 soft or broken or occurs in thin plates. A typical profile of San Joaquin 
 sandy loam, a red "iron" hardpan soil, is given in figure 6. 
 
 TYPE ^J^^^A^^<^lnJ^y^r^. LOCATION 7Wj^4*J^-i'^t*4A \/o£JIsm. _ 
 
 nCUEr $k%fo&££Zt: ELEVATION 25P_|ifC _ DRAINAGE S^4j^^%*ctn£<&£ 
 
 RAINFALL _//_^2^~^L _ NATIVE VE6ETATION JSvla^u _ _ _ USE _ T^Gi/UL — 
 
 ORIGIN ^^r^4^±-4^I^^AS^JL DEVELOPMENT OF PROFILE ~yt\^^S^_ -^tuithtyuL _ _ — 
 REMARKS _ "7t^_V\*>^-£^4jP4^-£*tJI _ — — _ — — — 
 
 /ia/u*^, trL ZS". 
 
 COLOR 
 
 ?^f4 
 
 STRUCTURE 
 
 GONS'STEKCE 
 AND 
 
 DENSITY 
 
 MISCELLANEOUS 
 ROOTS, STONES, COUCHETIONS, 
 PERMSABIi-VTt, ETC. 
 
 
 
 
 ">nff-o4_ , T\4s%JL 
 
 AcU I 
 
 VI. AjV^. 
 
 pJL'\S^L 
 
 ~#4 
 
 UOJL, 
 
 jggk 
 
 "MSjuXHaJ 
 
 lic^ur^n^Ke- 
 
 J^ 
 
 4l~k. 
 
 
 3E3? 
 
 
 <JLnA«_ 
 
 
 
 / at'v*ot*"«-»4. 
 
 
 frasa<c 
 
 -]QW>~*- 
 
 M 
 
 Fig. 6. — Profile description of San Joaquin sandy loam, a typical hardpan soil of 
 group IV. 
 
 GROUP V, STRONGLY WEATHERED SOILS WITH DENSE CLAY 
 SUBSOILS RESTING ON CONSOLIDATED MATERIALS 
 
 Soils of group V are common along the coastal plain of California. 
 Their value is relatively low because of the leached surface, the heavy- 
 textured subsoil, and particularly because of the hardpan-like substra- 
 tum which, although composed of sediments, is essentially rock-like in its 
 nature (fig. 7). Surface soils are normally somewhat acid in reaction. 
 There is usually an abrupt change from the surface layer to the heavy 
 dense clay subsoil, and after heavy rains these soils become temporarily 
 water-logged. 
 
18 
 
 University of California — Experiment Station 
 
 With two exceptions, the Stockton and Landlow, all the soil series so 
 far mapped occur on high terraces which have been subjected to con- 
 siderable erosion. The Stockton and Landlow soils occur on flat, poorly 
 drained plains, and instead of being sandy have heavy-textured surface 
 soils. 
 
 In this group the surface soils overlying the clay subsoils are usually 
 less than 15 inches in thickness, and the clay subsoil varies from 10 to 
 24 inches in thickness. Thus the consolidated substratum is found at 
 from 15 to 48 inches below the surface. 
 
 Fig. 7. — Profile of Olivenhain loamy fine sand from San Diego County, California. 
 Note the sandy surface soil lacking structure, the heavy-textured, dense subsoil, 
 which breaks up into columnar structure when dry, and the massive consolidated sub- 
 stratum. This is a typical soil of group V. (From Bui. 552.) 
 
 In rating the soils of this group for factor A the points considered are 
 the depth to the clay layer, the depth to the substratum, the nature of 
 the substratum, and the surface relief. The range in rating is from 20 to 
 40 per cent. Surface texture and other factors are handled under fac- 
 tors B and C. 
 
 Soils of the Olivenhain, Tierra, and Las Flores series, which are typ- 
 ical of this group, have similar sequence of horizons, and differ mainly 
 in color. A profile of Olivenhain loamy fine sand from the coastal plain 
 of San Diego County is given in figure 8. The factor-A rating of this 
 soil is 25 per cent. 
 
Bul. 556] 
 
 Index for Rating Value of Soils 
 
 19 
 
 TYPE J^-^c^La^ji^^y-i £^Ajx»<fL LOCATION _ _~_*£y _^_^ _"*_-_ _ e 'fc. _ t/> _.-£_*J_' 
 
 RELIEF _^^-_ J __ : ? , _ ct ELEVATION _ _f_P-__ — DRAINAGE _^^^ a _ Y _$_- _*°_ : _ J _"_' 
 
 RAINFALL _ i>_ IJ>1 _ _ NATIVE VEGETATION _Sho?£ ^*4 USE _ «_yt^r_: *f»*_ a, fp 4 '- 
 
 ORIGIN /^cx*^J&W«L. _ C £ V ELOPMENT OF PROFILE _^_>~_>*_^_' t _ _____ 
 
 REMARKS _ — _ _ — _ — _ — 
 
 
 
 
 
 
 - Jh$M 
 
 K-aMA\*t _jr. 
 
 LZSL 
 
 __ _ . 
 
 PROFILE 
 
 COLOR 
 
 TEXTURE 
 
 STRUCTURE 
 
 CONSISTENCE 
 
 AND 
 
 DENSITY 
 
 REACTION 
 
 MISCELLANEOUS 
 ROOTS, STONES, CONCRETIONS, 
 PERMEABILITY, ETC. 
 
 
 
 XUvL i&bmL 
 
 
 iWo_- 
 
 P HG.Z n 
 
 •<fc~" /vOtrCo> 
 
 0T T 
 
 m 
 
 ~3%tvcn*mj 
 
 12- " 
 
 
 'H 
 
 
 Ordbuici 
 
 7 ? 
 
 
 24- 
 
 
 3f- E 
 
 
 
 
 tnacAtAK. 
 
 
 
 
 
 
 
 48- 
 
 — - 
 
 
 60- 
 
 
 
 Fig. 8. — Profile description of Olivenhain loamy fine sand, typical of coastal plain 
 soils having dense clay subsoils (group V). 
 
 GROUP VI, SOILS DEVELOPED ON BEDROCK (PRIMARY 
 OR RESIDUAL SOILS) 
 
 Soils of group VI have been formed by the disintegration and decom- 
 position of the underlying parent bedrock (fig. 9). Shaw 6 has termed 
 them primary soils. They are also referred to in soil literature as resid- 
 ual soils. They are the hill lands of California, occupying a topography 
 that is rolling, hilly, or mountainous (fig. 13) . 
 
 Their characteristics are determined to a large extent by the character 
 of the parent bedrock and the rainfall of the region in which they occur. 
 Often they are shallow and stony. These factors, together with the topog- 
 raphy and surface configuration, determine their value. Because of their 
 slope, they are more difficult to farm than the terrace and valley lands. 
 The steep slopes have a tendency to erode badly, especially when culti- 
 vated. The normal progress of erosion is the main factor that keeps most 
 primary soils from reaching a mature stage of soil weathering. Most of 
 the primary soils have a moderate accumulation of clay in the subsoils as 
 a result of soil weathering, but not nearly so much as exists in soils of 
 groups III, IV, or V. Usually the upper portion of the underlying parent 
 bedrock has been softened by weathering action so that roots and mois- 
 ture have an opportunity to work their way down into the bedrock 
 through cracks and crevices for some distance. 
 
 6 Shaw, C. F. A definition of terms used in soil literature. 
 Sci.Proc. 5:38-64. 1928. 
 
 Intntl. Congr. Soil 
 
20 
 
 University of California — Experiment Station 
 
 . ;, . 
 
 Fig. 9. — Profiles of shallow primary soil (group VI), Sierra Nevada foothill district. 
 
 TYPE B*M*~4? ^^±. ^»2^y_ _ LOCATION SltstA^. Tl^oyJa. jW^."^lA«>S?l 
 
 RELIEF. J^^h ELEVATION -T^L-Af^ _ DRAINAGE _ l^WL^^Li^JL 
 
 RAINFALL 30_^>ycXsS- NATIVE VE6ETATION i?/Wj£t. QaA, _ USE J = ^r^o^^xxeLxi, __ 
 
 ORIGIN _T2^o^_A«^J^^ 4*142^ J3EVELOPMENT OF PROFILE 
 
 REMARKS 
 
 _ ~F ktriU U Hafcyz 61 t>S 
 
 
 
 
 STRUCTURE 
 
 r 
 
 (Mvdtan, 
 
 
 
 CONSISTENCE 
 
 AND 
 
 DENSITY 
 
 
 
 
 
 Fig. 10. — Profile description of Holland sandy loam in the Sierra Nevada foothills. 
 This is a primary or residual soil of group VI. 
 
 
 AU.JL * 
 
 -yicJbJttJL 
 
 MISCELLANEOUS 
 ROOTS, STONES. CONCRETIONS, 
 PERMEABILITY, ETC. 
 
 TZVVmuC&J? -try fr&vt&. 
 
 ~rzjLn*~*-*XLJl '9*1 K^&Zg. 
 
 S<r«v» ^oVU^JUi' 
 
 f<2ry 
 
Bul. 556] Index for Rating Value of Soils 21 
 
 Considerable variation is encountered in depth and stone content, and 
 such variations are considered in rating these soils. Typically, primary 
 soils are well drained and contain no alkali so that these factors do not 
 have to be considered under factor C. 
 
 Texture of the surface soil is largely governed by the type of parent 
 bedrock. Coarsely crystalline rocks, such as granites, usually give rise 
 to sandy soils, while the finer-textured rocks, such as the andesites, 
 weather into clay loam types. 
 
 Some of the better-known primary soils are those of the Holland, 
 Sierra, and Aiken series of the Sierra-Nevada foothills. The Aiken is the 
 very red primary soil derived mainly from andesitic parent bedrock, 
 while the other two are brown and red granitic soils. A profile descrip- 
 tion of a Holland sandy loam of the Sierra-Nevada foothill district is 
 given in figure 10. 
 
 The ratings given the primary soils are based on the depth of soil ma- 
 terial overlying bedrock, as follows : 
 
 Rating, in 
 per cent 
 Less than 1 foot- 20-25 
 
 1 to 2 feet 25-40 
 
 2 to 3 feet 40-60 
 
 over 3 feet 60-70 
 
 FACTOR B : TEXTURE OF SURFACE SOIL 
 
 Factor B rates the soil on the basis of the characteristics of the sur- 
 face soils, independent of the subsoils. It is a rating of the soil textures 
 and those other characteristics that are more or less dependent on tex- 
 ture, such as the consistence (hardness or softness) of the soil aggre- 
 gates, the porosity of the soil mass, the permeability to water, the tilth 
 (response to tillage operations), and similar characteristics or reactions. 
 These are so dominated by texture that a rating on the textural basis 
 will also express the general effect of these features. 
 
 Textural grades, designated in popular terms such as sandy loam, 
 loam, and clay loam, express the mass effect of the amounts of different- 
 sized grains that constitute the soil. The physical composition of a soil 
 can be accurately determined by a mechanical analysis which separates 
 the soil into grain-sized groups. The limits of the amounts of the grain- 
 sized groups present in any textural grade have been definitely estab- 
 lished. 
 
22 
 
 University of California — Experiment Station 
 
 TABLE 3 
 
 Textural Grades of Soils' 
 
 Grade 
 
 Coarse sand.. 
 
 Sand. 
 
 Fine sand 
 
 Very fine sand 
 
 Sandy loam. 
 
 Fine sandy loam 
 
 Very fine sandy loam 
 
 Loam.. 
 
 Definition* 
 
 Contains less than 20 per cent 
 silt and clay, and more than 
 35 per cent fine gravel and 
 coarse sand grain sizes, and 
 less than 50 per cent any other 
 grade. 
 
 Contains less than 20 per cent 
 silt and clay, and more than 35 
 per cent fine gravel and coarse 
 sand and medium sand, and 
 less than 50 per cent fine sand. 
 
 Contains less than 20 per cent 
 silt and clay, and more than 50 
 per cent fine sand, and less 
 than 25 per cent fine gravel 
 and coarse and medium sand. 
 
 Contains less than 20 per cent 
 silt and clay, and more than 50 
 per cent very fine sand, and 
 less than 25 per cent fine gravel 
 and coarse and medium sand. 
 
 Contains between 20 and 50 per 
 cent silt and clay, and more 
 than 25 per cent fine gravel 
 and coarse and medium sand, 
 and less than 35 per cent fine 
 or very fine sand. 
 
 Contains between 20 and 50 per 
 cent silt and clay, and more 
 than 50 per cent fine sand, and 
 less than 25 per cent fine gravel 
 and coarse and medium sand. 
 
 Contains between 20 and 50 per 
 cent silt and clay, and more 
 than 35 per cent very fine 
 sand, and less than 25 per cent 
 fine gravel and coarse and 
 medium sand. 
 
 Contains more than 50 per cent 
 total silt and clay, and less than 
 20 per cent clay, from 30 to 50 
 per cent silt, and from 30 to 50 per 
 cent sands. 
 
 Obvious characteristics 
 
 Sands are loose and granular. The indi- 
 vidual grains can readily be seen and felt. 
 Squeezed in the hand when dry the ma- 
 terial will fall apart when the pressure is 
 released. Squeezed when moist, it will 
 form a cast but will crumble when 
 touched, although fine sand and very fine 
 sand have a certain amount of cohesion 
 when moist. 
 
 Contains much sand but which has enough 
 silt and clay for coherence, gritty feel; 
 sand grains can be seen. Squeezed when 
 dry will form a cast which will readily fall 
 apart, but if squeezed when moist a cast 
 can be formed that will bear careful 
 handling without breaking. Classed as 
 coarse, medium, fine or very fine sandy 
 loam, depending on the proportion of the 
 different-sized particles that are present. 
 
 Even mixture of different grades of sand, 
 and of silt and of clay. Mellow, of some- 
 what gritty feel, yet fairly smooth and 
 rather plastic. Squeezed when dry it will 
 form a cast that will bear careful han- 
 dling, while the cast formed by squeezing 
 the moist soil can be handled rather freely 
 without breaking. 
 
 * For ratings see table 4, page 38. 
 
 t The grades are defined on the basis of the amount of the several grain-sized groups of particles found 
 in them upon mechanical analysis. For the sizes of the soil-particle groups see footnote 7, page 24. 
 
Bul. 556] 
 
 Index for Rating Value of Soils 
 
 23 
 
 TABLE 3— (Concluded) 
 
 Grade 
 
 Silt loam.. 
 
 Clay loam. 
 
 Silty clay loam 
 
 Clay. 
 
 Silty clay. 
 
 Adobe clay or clay 
 adobe 
 
 Definition 
 
 Contains more than 50 per cent 
 total silt and clay, and less than 
 20 per cent clay, more than 50 per 
 cent silt, and less than 50 per cent 
 sands. 
 
 Contains more than 50 per cent 
 total silt and clay, and 20 to 30 
 per cent clay, and less than 50 
 per cent silt or sand. 
 
 Contains more than 50 per cent 
 total silt and clay, and 20 to 30 
 per cent clay, more than 50 per 
 cent silt, and less than 30 per cent 
 sand. 
 
 Contains more than 30 per cent 
 clay, and less than 50 per cent silt 
 or sands. 
 
 Contains more than 30 per cent 
 clay, more than 50 per cent silt, 
 and less than 20 per cent sands. 
 
 Contains more than 30 per cent 
 clay, particularly the ultra or col- 
 loidal-clay particles, and less 
 than 50 per cent silt or sands. 
 
 Obvious characteristics 
 
 Moderate amount of the fine grades of sand 
 and only a small amount of clay, over half 
 of the particles being of the size called 
 "silt." When dry it may appear cloddy 
 but the lumps can readily be broken, and 
 when pulverized it feels soft and floury. 
 Either wet or dry the soil will form a cast 
 that can be freely handled without break- 
 ing. If squeezed between the thumb and 
 finger it will not "ribbon," but will give a 
 broken appearance. 
 
 A clay loam in the field is dense and com- 
 pact, and breaks into clods or lumps, 
 which when dry are hard to break. When 
 the moist soil is pinched between the 
 thumb and finger it will form a thin "rib- 
 bon" that will break readily, barely sus- 
 taining its own weight. Moist soil is plastic 
 and will form a cast that will bear much 
 handling. When kneaded in the hand it 
 does not crumble readily but tends to 
 work into a heavy compact mass. 
 
 Silty clay loam contains more of the par- 
 ticles termed "silt" so that the soil is less 
 plastic than the clay loam. 
 
 Dense and compact, forming very hard 
 lumps or clods when dry. Composed of 
 very fine particles which when wet stick 
 together to make a very putty-like and 
 plastic mass. When the moist soil is 
 pinched out between the thumb and 
 fingers it will form a long flexible "ribbon." 
 
 Silty clay contains more of the particles 
 termed "silt" so that the soils break down 
 more readily than a clay. 
 
 In addition to characteristics of clay, adobe 
 clays contract on drying, producing large 
 cracks and blocks. Secondary cracking 
 may cause them to break into smaller 
 fragments. The term "adobe" alone, 
 refers to this structure produced by 
 shrinkage on drying. 
 
24 University of California — Experiment Station 
 
 The various textural grades of soils are listed in table 3, with the 
 amounts of the grain-sized groups (determined by mechanical anal- 
 ysis), 7 and some of the obvious physical characteristics of the various 
 soil textures. The major textural grades give very characteristic re- 
 sponses when rubbed between the thumb and fingers, and when kneaded 
 and molded while wet. With practice, the textural grade of a soil can be 
 approximated by this hand test, which aids in determining the texture 
 when soil maps are not available. 
 
 Texture or physical composition controls, to a large degree, the water- 
 holding capacity, permeability to moisture, ease of tillage, plasticity, the 
 stickiness of the soil when wet, and the friability and hardness when dry. 
 Soils having ideal conditions from the textural standpoint as reflected 
 in these physical characteristics are rated at 100 per cent in factor tB. 
 Soils having less favorable textures are rated according to their relative 
 order. Soils with a large percentage of sand or gravel are relatively low 
 in the plant nutrients and do not retain moisture so well as do those of 
 finer texture. At the other extreme heavy-textured soils, those having a 
 high percentage of clay particles, are more difficult to handle and have 
 other disadvantages, although they may contain a maximum of moisture 
 and plant nutrients. 
 
 It must be borne in mind that the ratings on soil texture are on a rela- 
 tive basis and can be varied to some degree as conditions may warrant. 
 
 MEDIUM-TEXTURED SOILS Rating, in 
 
 per cent 
 
 Fine sandy loam 100 
 
 Loam 100 
 
 Silt loam 100 
 
 Sandy loam 95 
 
 Coarse sandy loam 90 
 
 Loamy sand 80 
 
 The medium-textured soils are given the highest rating since they do 
 not contain an excess of either the sand or the clay, have a medium-soft 
 consistence, take water readily yet have a good water-holding capacity, 
 are friable and easy to cultivate, do not readily puddle or form clods, 
 and in general are most easily maintained in a condition of good tilth. 
 
 7 Eight grain-sized groups have been adopted by the United States Department 
 of Agriculture with the effective diameter of the particles as indicated below: 
 Diameter in millimeters Name of size group 
 
 2.0 - 1.0 fine gravel 
 
 1.0 — 0.5 coarse sand 
 
 0.5 - 0.25 sand 
 
 0.25 - 0.10 fine sand 
 
 0.10 - 0.05 very fine sand 
 
 0.05 - 0.005 silt 
 
 0.005 - 0.002 coarse clay 1 
 
 less than 0.002 ultra or colloidal }• clay 
 
 clay J 
 
Bul. 556] Index for Rating Value of Soils 25 
 
 Fine sandy loam, 8 loam, and silt loam are given the highest textural rat- 
 ing. They have a fairly high water-holding capacity (18 to 40 per cent 
 by dry weight), and a high amount of available water. These are the 
 best-textured soils for such intensive crops as vegetables, which have to 
 secure their moisture and plant nutrients from a relatively small volume 
 of soil. Sandy loams are rated slightly lower since they do not have the 
 power to hold as much moisture, and so do not have quite the range in 
 use that the fine sandy loams, loams, or silt loams have. 
 
 Coarse sandy loams have a still lower water-holding capacity and 
 usually less organic matter and plant nutrients, and so are rated lower 
 than the sandy loams. 
 
 Loamy sands hold 5 to 9 per cent of moisture as against 10 to 13 per 
 cent by sandy loams. For most crops they do not have as much potential 
 value as the slightly heavier-textured soils even though they are easy to 
 handle at any moisture content. They have a fairly high value for cer- 
 tain specialized crops that are grown along the coast, such as winter 
 squash, peas, etc. 
 
 MEDIUM-HEAVY-TEXTURED SOILS Rating, in 
 
 per cent 
 
 Silty clay loam 90 
 
 Clay loam 85 
 
 Silty clay loam and clay loam soils have a high water-holding capacity 
 (25 to 40 per cent), but puddle rather easily and have a tendency to be- 
 come hard on drying. Their general range in cropping adaptation is 
 lower than the loam or silt loam since they take water more slowly, are 
 harder when dry, and more power is required in the use of tillage imple- 
 ments. Silty clay loam is somewhat easier to till than the clay loam be- 
 cause of the higher silt content. Certain calcareous types of both the 
 silty clay loam and clay loam are more friable owing to the high lime 
 content. As a general rule, soils of these textures are fertile and highly 
 productive in California. 
 
 HEAVY-TEXTURED SOILS Rating, in 
 
 per cent 
 
 Silty clay 60 
 
 Clays and adobe clays 50-70 
 
 8 In classifying the yields of oranges on different soil types in southern Cali- 
 fornia, Vaile states that "the groves planted on medium-textured soil (fine sandy 
 loam) gave the highest average yield." (Vaile, Roland S. Survey of orchard prac- 
 tices in the citrus industry of southern California. California Agr. Exp. Sta. Bul. 
 374:11, table 6. 1924.) It is significant that only about 5 per cent of the groves 
 were planted on very light soil (sand) and that these groves produced 30 per cent 
 less than those on medium-textured soil, while only from 5 to 10 per cent of the 
 groves were planted on medium-heavy soil and these produced 10 per cent less 
 than those on the medium-textured soil. 
 
26 University of California — Experiment Station 
 
 The properties of silty clay and clay soils are largely governed by the 
 character of the clay particles that make up from 30 to 60 per cent of the 
 soil mass. Often a large proportion of the clay particles are of the ultra- 
 clay or colloidal-clay size and exhibit the physical properties of colloids. 
 
 Clay soils are cold and sticky when wet, and very hard when dry. The 
 high clay or colloidal content impedes the movement of water, causing 
 water-logged conditions in wet weather and lack of available moisture 
 during the dry season. When dry, they shrink and crack, frequently 
 breaking into large, hard blocks with wide cracks between, giving the 
 structure known as "adobe clays." As a result they are not so desirable as 
 the lighter-textured soils. They are best adapted to crops, such as grain 
 and rice, for which heavy machinery is needed. 
 
 Most clays are improved by the addition of lime or other flocculating 
 materials, which cause the soil to form aggregates with definite struc- 
 tural properties, and results in a decrease in the plasticity and hardness 
 of the mass. This materially increases the ease of tillage. On the other 
 hand, certain of the alkali salts exert a deflocculating effect on the soil 
 mass, making it less pervious and more difficult to till. Organic matter 
 acts very much in the same way as lime on clay soils, but the amount has 
 to be high and frequently applied in order to make much improvement 
 in the physical condition. 
 
 Clays generally are high in plant nutrients, but physical factors such 
 as plasticity, penetrability, and drainage overshadow these desirable 
 chemical characteristics. 
 
 Silty clay is a little more friable owing to the higher content of silt. 
 
 LIGHT-TEXTURED SOILS Rating, in 
 
 per cent 
 
 Very fine sand 80 
 
 Fine sand 65 
 
 Sand 60 
 
 Wind-blown sands 20-70 
 
 The sands listed above differ in the relative size of the sand particles 
 making up the soil. All have less than 20 per cent total silt and clay par- 
 ticles. The large proportion of sand particles renders these soils open 
 and friable. Water percolation through the soil mass is fairly rapid and 
 is liable to be excessive in the coarser sands. Air moves rapidly through 
 sandy soils and they warm up more quickly in the spring than do heavier- 
 textured soils. This factor renders them desirable for certain specialized 
 truck crops. 
 
 The wide range in the rating of wind-blown sands — 20 to 70 — is due to 
 the great variation in the surface configuration of this type of material. 
 Soils of the Rositas, Coachella, and Oakley series are typical examples 
 
Bul. 556] Index for Rating Value of Soils 27 
 
 of wind-blown material. The shifting of sand by wind action causes 
 serious difficulties in certain instances. The cost of leveling this type of 
 material for irrigation is relatively high. 
 
 The available plant nutrients of sands are low. Large applications of 
 organic material in the form of manures or covercrops are necessary to 
 maintain yields on them, and frequent application of fertilizers is neces- 
 sary in order to maintain their valne for intensive cropping. Moisture 
 must be available at regular intervals during the growing season. This 
 interval and application is necessarily relatively short since the mois- 
 ture-holding capacity of the sands is small compared with that of the 
 medium-textured soils. The normal moisture capacity will vary from 
 2-3 per cent in the coarse sand up to 7-10 per cent for the very fine sand. 
 Thus it can readily be seen that the value decreases with the coarseness 
 of the soil. 
 
 Sands occurring where there is a high rainfall are leached of their 
 plant nutrients and are usually of very low productive value. For- 
 tunately, the area of such soils in California is limited largely to the 
 northern coast line. Some of the southern coastal plain sands have been 
 moderately leached, but the arid and semiarid sands are fairly good pro- 
 ducers when moisture and sufficient organic material are present. 
 
 GRAVELLY OR COBBLY SOILS Rating, in 
 
 per cent 
 
 Gravelly fine sandy loam 70 
 
 Gravelly loam 70 
 
 Gravelly silt loam 70 
 
 Gravelly sandy loam 65 
 
 Gravelly clay loam 55 
 
 Gravelly clay 35 
 
 Gravelly sand 20-30 
 
 The presence of gravel in a soil interferes with tillage operations, and, 
 especially in the case of the lighter-textured soils, materially lowers 
 their water-holding power. Suggested ratings are given above. These 
 may have to be lowered or raised according to the amount of gravel 
 present in the soil mass. 
 
 STONY SOILS Rating, in 
 
 per cent 
 
 Stony fine sandy loam 70 
 
 Stony loam 70 
 
 Stony silt loam 70 
 
 Stony sandy loam 65 
 
 Stony clay loam 60 
 
 Stony clay 35 
 
 Stony sand 10-40 
 
 Stone in a soil interferes with tillage and all farm operations, and 
 lowers the water-holding capacity and the volume of actual soil from 
 which plants can secure food. The rating of soils containing enough 
 
28 University of California — Experiment Station 
 
 stone to interfere with farm operations should be lowered. Suggested 
 ratings are given above where the soils have been mapped under such 
 type names in the soil surveys. 
 
 FACTOR C : SOIL-MODIFYING CONDITIONS 
 
 As mentioned previously, a number of other conditions may exist 
 that modify the value of the soil. These are generally determined by 
 field observations or by a few simple field tests. They are listed with 
 suggested ratings under the following headings and in table 4 (page 38) . 
 
 DRAINAGE 
 
 Soils having a high water table or a fluctuating ground-water level 
 are obviously of lower value than those which are well drained. The 
 past drainage history and the prospects of the soil's becoming water- 
 logged under future utilization should have careful consideration in any 
 system of soil evaluation. Many of the dark-colored alluvial soils are 
 poorly drained, especially those at the lower ends of the alluvial fans 
 where water has accumulated by seepage from the higher lands. Drain- 
 age conditions are divided into four classes, each given a rating. 
 
 1. Well Drained .... 100 per cent. — Soils are considered well drained 
 where the water level is deep and there is no probability of the soil's be- 
 coming water-logged. 
 
 2. Fair Drainage .... 80-90 per cent. — Drainage is considered fair 
 where the water table is sufficiently below the surface so that little crop 
 injury is experienced, and where any excessive water can be taken care 
 of through artificial drains at a low or moderate cost. Areas where there 
 may be some shallow flooding for brief periods are also placed in this 
 class. 
 
 3. Moderately Water-logged .... 40-60 per cent. — Soils are consid- 
 ered moderately water-logged where the permanent water table is suf- 
 ficiently close to the surface so that only the shallow-rooted crops can be 
 grown. 
 
 4. Badly Water-logged .... 10-40 per cent. — Land is considered badly 
 water-logged where the ground water is permanently close to the sur- 
 face, so that agriculture is limited to very poor wild grasses. 
 
 ALKALI 
 
 Alkali is often the limiting factor governing the value of desert soils. 
 It consists of an excess of soluble salts that have accumulated in the soil 
 because of poor drainage and excessive surface evaporation (fig. 11). 
 
Bul. 556] 
 
 Index for Rating Value of Soils 
 
 29 
 
 Chemically, they may be sodium chloride, sodium sulfate, sodium car- 
 bonate, etc. Alkali is not normal to humid soils of the eastern part of the 
 United States since it cannot accumulate where there is a high rainfall 
 and the soils are leached. 
 
 Recognizing the importance of alkali, careful studies are made of this 
 problem in the soil surveys of desert areas. The harmfulness of alkali is 
 dependent not only on the amount present in the soil, but on its position 
 in the profile, its chemical composition, the texture of the soil, and the 
 
 
 Fig. 11. — White alkali crust, with a native cover of grease wood. This soil is of no 
 value for agriculture because of the high alkali content. (Photograph by W. W. 
 Weir.) 
 
 amount of moisture present. Plants do not tolerate a great deal of alkali 
 if it is concentrated as a surface crust, or if it is of the "black" variety 
 (sodium carbonate) , or if it is concentrated in a dry soil. 
 
 In mapping the alkali of an area such lands have often been classed 
 in four grades 9 with reference to the total content, the kind of alkali, 
 and the visible conditions such as the appearance of the crop or the pres- 
 ence of alkali-tolerant weeds growing on the land (fig. 11). 
 
 1. Alkali-free: 100 per cent. — This grade includes areas whose salt 
 content is less than 0.2 per cent and so evenly distributed throughout 
 the soil profile as to be noninjurious to crops. 
 
 2. Slightly Affected Areas: 90 per cent. — This grade includes areas 
 whose salt content is usually between 0.2 and 0.6 per cent, but so dis- 
 tributed throughout the soil profile as to have only slight effect on crops. 
 
 9 Strahorn, A. T., et al. Soil survey of the El Centro area, California. U. S. Dept. 
 Agr. Bur. Soils, pp. 641-716. 1918. 
 
30 University of California — Experiment Station 
 
 3. Moderately Affected Areas: 60 per cent. — This grade includes land 
 with a salt content of less than 2 per cent, which is so distributed in the 
 soil profile as to depress the yields of crops, but not prevent their growth. 
 Soils with a much smaller amount of black alkali are rather toxic. 
 
 4. Strongly Affected Areas: 5-25 per cent. — Crops are limited and to 
 a large degree prohibited by the alkali content in these areas. The total 
 amount of salts may vary from 1 to 2 per cent or more, as an average 
 throughout the profile, but is usually high in the surface foot — often 
 over 3 per cent. Some of these areas have practically no value for agri- 
 culture. Soils with much smaller amount of black alkali (sodium car- 
 bonate) may be rather toxic and should be placed in this grade. 
 
 ACIDITY 
 
 A number of soils exist in California which are acid in reaction (table 
 1, page 7). The rating of acid soils is reduced according to the degree 
 of acidity, for most crops are injured by excessive acidity of the soil. 
 Suggested ratings vary between 60 and 95 per cent. The hydrogen-ion 
 concentration (usually expressed as pH) of soils is a measure of the in- 
 tensity of acidity. Soils with a pH of about 7.0 are said to be neutral in 
 reaction ; those with a pH of 6.0-6.5, slightly acid ; those with a pH of 
 4.5-6.0, moderately acid; and those with a pH below 4.5, very acid. 
 Alkaline soils have a pH of over 7.0. Soil acidity can be quickly and 
 easily determined by simple tests. A number of field testing kits, satis- 
 factory for approximate determinations of soil reaction, are available. 
 
 INFERTILITY 
 
 Information can usually be secured about the general fertility of a 
 soil by studying the past cropping history. Where a soil is of lowered 
 fertility, its rating can be lowered by applying a factor here to take care 
 of this. In most cases this will be between 80 and 95 per cent, although 
 in some extreme cases a lower number should be given. 
 
 A routine chemical analysis does not give very much information re- 
 garding the adaptability of soils to crops, or methods of fertilization, 10 
 so that field observations on the cropping history and the native vegeta- 
 tion growing on the soil must be used to supplement other information 
 regarding the availability of plant nutrients. Often valuable informa- 
 tion can be secured by studying the distribution of crops on each soil 
 series or soil type. Where agriculture has been long established in a re- 
 
 !o Hoagland, D. R. Fertilizer problems and analysis of soils in California. Cali- 
 fornia Agr. Exp. Sta. Cir. 317:1-16. 1930. 
 
Bul. 556] Index for Rating Value of Soils 31 
 
 gion this information is of great value in rating the productive capacity 
 of the respective soils. "Worn out" or infertile soils can be determined 
 by such a study. 
 
 STRATIFIED SUBSOILS (GRAVELLY LAYERS OR 
 STRATIFIED CLAY LAYERS) 
 
 Where moisture is a limiting factor in crop growth, the presence of 
 gravelly layers in the alluvial soils is a distinct handicap, since such 
 subsoils are of leachy character with little power of holding moisture 
 for crop use. These gravelly pockets, or subsoil layers, are most common 
 in soils of the Tujunga, Hanford, Yolo, and Elder series, which are of 
 fairly recent deposition. Such pockets are a result of the deposition of 
 gravelly material by fast-moving water, and later deposition of finer and 
 better surface soil over it. These "pockets" are not obvious from surface 
 soil examination, except that crops may appear wilted where there is a 
 deficiency of moisture. The rating given soils having such conditions will 
 naturally vary, although a rating of 80-95 per cent will take care of most 
 cases. 
 
 Certain alluvial soils having heavy-textured layers in the subsoils 
 should be discounted' in value to some extent. Fairly large areas of soils 
 having such conditions exist in the Imperial Valley. A rating of 80-95 
 per cent is suggested to cover such conditions. 
 
 SHALLOW PHASES OF ALLUVIAL SOILS 
 
 In certain extreme cases alluvial soils may be only 2 or 3 feet deep over 
 a flat substratum or bedrock. A rating of 50-60 per cent might be given 
 for a 2-foot depth of soil, and a rating of approximately 70 per cent for 
 alluvial soils about 3 feet in depth. 
 
 ERODED SOILS 
 
 All soils located on slopes erode or wash to some extent. Under certain 
 conditions of rainfall and removal of the vegetative cover by cultiva- 
 tion, overgrazing, lumbering, and fire, this is hastened, and the soils 
 erode to such an extent that their value is materially lowered 11 (fig. 12) . 
 Soils eroded to a moderate extent might be given a rating of 80-95 per 
 cent, while the badly eroded soils, such as those mapped as eroded 
 phases, should be given a much lower figure. 
 
 ii Weir, Walter W. Soil erosion in California: its prevention and control. Cali 
 fornia Agr. Exp. Sta. Bul. 538:45. 1932. 
 
32 University of California — Experiment Station 
 
 STEEP PHASES 
 
 Soils occurring on steep slopes are difficult to till, and should be low- 
 ered in their rating. Rough mountainous slopes are of still less value. A 
 range in the rating may be 60-80 per cent for soils occurring on slopes 
 that are fairly difficult to till, and 20-30 per cent for soils on steep moun- 
 tainous slopes. 
 
 ,-i 
 
 Fig. 12. — Eecent erosion cuts 2 to 3 feet in depth have materially lowered the value 
 of this field. Note deposition of eroded soil material on the flat. (From Bui. 538.) 
 
 NONAGRICULTURAL MATERIALS 
 
 In most of the soil surveys there is a miscellaneous class of materials 
 that is not classed with the soil series or soil types, but classed under a 
 miscellaneous group. This has little value from an agricultural stand- 
 point. For purposes of rating them, these are given an index, although 
 they really belong in a system of land classification rather than in a soil 
 category. 
 
 Nonagricultural materials which are mapped under miscellaneous 
 group in soil surveys are as follows : 
 
 1. Rough Mountainous Land: 5-10 per cent. — This class of land 
 usually occurs on rougher mountainous topography; it is often good 
 grazing land (fig. 13). 
 
 2. Scabland: 5 per cent. — Scabland consists of fairly recent lava 
 flows ; contains small patches of soil (fig. 14) ; it is of very little agricul- 
 tural value even for grazing. 
 
Bul. 556] 
 
 Index for Rating Value of Soils 
 
 33 
 
 Rough Broken Land: 5 per cent. — Rough broken land consists of 
 steep slopes, eroded slopes, gullies, and canyon walls, and contains very 
 small areas of arable land. 
 
 3. Riverwash : 1-5 per cent. — Riverwash consists of sandy, gravelly, 
 cobbly, or stony deposits of stream channels; subject to erosion and 
 overflow ; of no agricultural value. 
 
 Fig. 13. — Eough mountainous and rough stony land. Note small cleared area of 
 primary soil (group VI soils). (From Bul. 552.) 
 
 Fig. 14. — Scabland: a very thin layer of soil weathered from fairly recent lava 
 flow. It is of very low value. (Photograph from C. F. Shaw.) 
 
 Placer Diggings and Tailings: 1-5 per cent. — Areas where placer- 
 mining operations have left the surface covered with stone and gravel 
 are placed in this class. 
 
 Tidal Marsh: 1-5 per cent. — Tidal marsh lands are lands subject to 
 inundation by tidal action ; they are low, flat, and highly saline. 
 
34 University of California — Experiment Station 
 
 Coastal Beach: 1-5 per cent. — This class applies to sloping beaches of 
 sand, gravel, or stone. 
 
 Dunesand: 1-5 per cent. — Dnnesand consists of areas of sand on 
 dunes or ridges ; in more or less constant movement with wind. 
 
 Rough Stony Land: 1-5 per cent. — This class includes rough, stony 
 slopes (fig. 15). The presence of excessive amounts of stone and large 
 rocks or boulders is the dominant factor. 
 
 CALCULATION OF THE INDEX 
 
 To use this index method for rating soils it is obviously necessary to 
 know the characteristics of the soils to be rated. This information may 
 be obtained directly by adequately exploring the soil and subsoil to a 
 depth of 6 or more feet throughout the whole area to be rated, supple- 
 menting this exploration by field and laboratory studies to determine the 
 less obvious characteristics of the soil. This would require much time and 
 patient investigation, as well as a considerable degree of training in soil 
 studies. Most of the needed information can be obtained from the soil 
 maps and reports if the area to be rated has been covered by the soil 
 survey. The information available in these surveys has already been 
 discussed to some extent, and the Appendix gives further information 
 and lists the areas on which surveys have been completed and are 
 available. 
 
 As the soil maps are usually published on the scale of 1 inch to the 
 mile, it is difficult to show on the maps soil bodies that are less than 5 
 acres in area. Hence in rating any area it is essential that the informa- 
 tion supplied by the soil surveys be supplemented by direct field exami- 
 nation to ascertain the less extensive and more intimate characteristics 
 of the soils, and particularly the conditions included in factor C. 
 
 From experience in the use of the index it is suggested that the se- 
 quence given herewith be followed. 
 
 1. Ascertain the characteristics of the soil profile and especially those 
 of the subsoil and substratum, from soil-survey data and field studies. 
 Determine the group in which the soil belongs and develop the rating 
 for factor A. 
 
 2. Ascertain the textural characteristics of the surface soils, checking 
 by careful field observations to determine the direction of any local 
 variation from the typical texture. From these studies develop the rat- 
 ing for factor B. 
 
 3. Ascertain the presence or absence of alkali, poor drainage, or other 
 soil-modifying conditions. These are more variable in occurrence and 
 extent than the characteristics that determine factors A and B, and re- 
 
Bul. 556] 
 
 Index for Rating Value of Soils 
 
 35 
 
 quire much more field investigation to determine the intensity of local 
 conditions. From the results of this study, develop the rating for factor 
 C. Unless some specific unfavorable factor is present, the rating for 
 factor C should be 100 per cent. 
 
 k% 
 
 A 
 
 Fig. 15. — Rough stony land, nonagricultural class. It 
 supports growth of brush and a few trees. (Photograph by 
 C. F. Shaw.) 
 
 The final soil index is then obtained by multiplying A times B times C. 
 The values and limits assigned to the several divisions of each of the 
 three factors are summarized in table 4 (page 38). 
 
 SOIL RATING FOR A TRACT OF LAND 
 
 When a tract of land is to be rated, the soil survey, if available, is con- 
 sulted, and a field examination is made. On the basis of these, a soil map 
 such as that shown in figure 16 is prepared. The index for each soil type 
 in the tract is calculated separately, and then a rating for the entire 
 
36 University of California — Experiment Station 
 
 tract is calculated by weighting each soil index according to the propor- 
 tion of the acreage of that soil in the tract. Various tracts of land can be 
 compared by the use of these figures. 
 
 For the tract shown in figure 16, the steps in calculation would be as 
 follows : 
 
 1. Index for Hfsl, Hanford fine sandy loam : This soil is granitic fine 
 sandy loam of alluvial origin with no compaction or clay accumulation 
 in the subsoil, more than 6 feet in depth, well drained, and has no alkali. 
 It is of high productive value. Ratin in 
 
 per cent 
 
 Factor A: Hanford Series, group 1 100 
 
 Factor B: tine sandy loam (medium-textured soil) 100 
 
 Factor C: has no other modifying soil factors 100 
 
 ABC 
 
 Index rating = 100% X 100% X 100% = 100% 
 
 2. Index for CSiCl, Chino silty clay loam : This is dark gray alluvial 
 soil of granitic origin, with gray to dark gray subsoils which are cal- 
 careous. The soil is more than 6 feet in depth, but has a water table at a 
 depth of 3 feet from the surface. Rating in 
 
 per cent 
 
 Factor A: Chino Series, group 1 100 
 
 Factor B: silty clay loam (medium heavy) 90 
 
 Factor C: moderately water-logged 60 
 
 ABC 
 
 Index rating = 100% X 90% X 60% = 54% 
 
 3. Index for Hstl, Holland stony loam : This is brown primary soil 
 from granitic parent material. Bedrock is at an average depth of 3 
 feet. A considerable number of stones occur throughout soil mass. The 
 surface is gullied to some extent. Rating, in 
 
 per cent 
 
 Factor A: Holland Series, group VI (depth 3 feet) 60 
 
 Factor B: stony loam (stony) 70 
 
 Factor C: eroded surface 80 
 
 ABC 
 
 Index rating = 60% X 70% X 80% =33% 
 
 4. Index for R, rough stony land : The area consists of extremely stony 
 slopes, and is of little value. 
 
 Index rating = 2% 
 
Bul. 556] 
 
 Index for Rating Value of Soils 
 
 37 
 
 5. The index for the entire tract shown in figure 16 may then be cal- 
 culated according to the acreage of each soil, as follows : 
 
 Soil Index Acreage 
 
 Hanford fine sandy loam 100 X 95 = 9,500 
 
 Chino silty clay loam 54 X 10 = 540 
 
 Holland stony loam 33 X 65 = 2,145 
 
 Rough stony land 2 X 30 = 60 
 
 Total 200 12,245 
 
 12,245 
 
 Tract rating c= = 61. 
 
 200 
 
 SOIL MAP Or SMITH TRACT 
 
 SCALE IN FEET 
 
 =5= 
 
 ••.. 
 
 
 7? 
 
 
 HstL 
 
 
 
 ft 
 
 Htsl 
 
 ■ ■ 
 
 Hi 
 ii 
 ii 
 II 
 II 
 
 
 / "•**•., 
 
 \ 
 
 II 
 II 
 II 
 II 
 
 / 
 
 HslL 
 
 CSiCL "•-.. 
 
 II 
 Ii 
 II 
 
 
 
 LEGEND 
 
 ■ Main roads 
 
 —== Secondary roads 
 
 ■■ Buildings 
 
 '•""■ Soi/ boundary 
 Soils 
 
 nfsl nan ford -fins, sandy loam 
 
 CSiCL Chi no si liy clay loan) 
 
 Hsi'L Hoi land stony loam 
 
 /? Hough stony land 
 
 Fig. 16. — Soil map of a tract of land, which is made by 
 field examination. The figures listed below give the types, 
 their acreage, index, and grading. 
 
 Types Acreage Index Grade 
 
 Hanford fine sandy loam 95 100 1 — Excellent 
 
 Chino silty clay loam 10 54 3 — Fair 
 
 Holland stony loam 65 33 4 — Poor 
 
 Rough stony land 30 2 5 — -Very poor, non- 
 
 agricultural 
 
38 
 
 University of California — Experiment Station 
 
 TABLE 4 
 
 Soil Eating Chart— For Eating or Judging the Agricultural Value of Soils 
 (Soil Index Eating = Factor A x Factor B x Factor C) 
 
 Factor A, 
 
 Rating of soils on basis of character 
 
 of profile 
 
 Factor B, 
 
 Rating of soils on basis of surface 
 
 texture 
 
 Factor C, 
 Rating of conditions and char- 
 acteristics of the soil which 
 modify its suitability for utili- 
 zation in plant production 
 
 Soil group 
 
 Rating, 
 
 in 
 per cent 
 
 Texture 
 
 Rating, 
 
 in 
 per cent 
 
 Condition 
 
 Rating, 
 
 in 
 per cent 
 
 I. Unweathered or slightly 
 weathered secondary 
 
 95-100 
 
 Medi ikm-text ured : 
 
 100 
 100 
 100 
 95 
 90 
 80 
 
 Drainage: 
 
 100 
 
 
 
 80-90 
 
 
 
 moderately water- 
 
 
 II. Moderately weathered 
 secondary soils 
 
 80-95 
 
 
 
 40-60 
 
 coarse sandy loam 
 
 badly water-logged .... 
 
 
 III. Strongly weathered 
 
 40-80 
 
 10-40 
 
 Alkali: 
 
 
 secondary soils with 
 dense clay subsoils, 
 developed on uncon- 
 solidated parent ma- 
 
 
 
 Medium-heavy textured: 
 
 90 
 85 
 
 100 
 
 slightly affected 
 
 moderately affected . 
 strongly affected 
 
 90 
 
 
 60 
 
 
 
 terial 
 
 Heavy-textured: 
 
 65 
 50-70 
 
 5-25 
 
 IV. Maturely weathered 
 secondary soils with 
 
 5-10 
 10-20 
 20-30 
 30-40 
 40-60 
 
 Acidity: 
 according to degree- 
 
 
 clay and adobe clay 
 
 60-95 
 
 hardpan : 
 Hardpan less than 1 foot 
 
 Light-textured: 
 
 80 
 
 65 
 
 60 
 
 20-70 
 
 Infertility: 
 according to degree.. 
 
 60-95 
 
 
 
 1-2 feet 
 
 Stratified subsoils 
 
 60-95 
 
 
 
 2-3 feet .. 
 
 Shallow phases of allu- 
 vial soils: 
 
 
 3-4 feet 
 
 
 
 
 
 
 4-6 feet 
 
 Gravelly or cobbly: 
 gravelly fine sandy 
 
 70 
 70 
 70 
 65 
 55 
 35 
 20-30 
 
 
 
 50-60 
 
 V. Strongly weathered 
 
 20-40 
 
 
 70 
 
 
 
 
 
 Eroded soils : 
 
 
 subsoils resti ng on con- 
 
 
 
 gravelly silt loam 
 
 gravelly sandy loam 
 
 gravelly clay loam 
 
 80-95 
 
 solidated material 
 
 
 30-80 
 
 
 20-25 
 25-40 
 40-60 
 60-70 
 
 
 
 VI. Primary soils under- 
 laid by bedrock: 
 
 Steep phases: 
 fairly steep 
 
 60-80 
 
 Depth less than 1 foot... 
 1-2 feet 
 
 gravelly sand 
 
 steep 
 
 20-30 
 
 2-3 feet 
 
 Stony: 
 stony fine sandy loam. 
 
 70 
 70 
 70 
 65 
 60 
 35 
 10-40 
 
 
 
 
 
 
 
 
 
 
 
 stony sandy loam 
 
 
 
 
 
 
 
 
 
 
 
 Miscellaneous nonagricultural material 
 
 Type 
 
 Description 
 
 Rating in 
 per cent 
 
 Rough mountainous land 
 
 
 5-10 
 
 
 5-10 
 
 
 Steep slopes, eroded slopes, gullies, and canyon walls 
 
 5-10 
 
 
 1- 5 
 
 
 
 1- 5 
 
 
 Tidal lands 
 
 1- 5 
 
 
 
 1- 5 
 
 
 
 1- 5 
 
 
 
 
Bul. 556] Index for Rating Value of Soils 39 
 
 SUMMARY 
 
 Soils vary in their productive capacity. 
 
 There is need for some method of comparing the relative productive 
 capacity of different soils, especially in California where such a large 
 number of widely divergent soil conditions exist. Such a soil rating or 
 index would be useful in land classification and land evaluation. 
 
 In this paper the term "index for rating soils" is used to express this 
 relative rating. Soils having the highest productive capacity (from a 
 study of the soil under field conditions) are rated at 100 per cent. 
 
 The rating is based on the study of three general factors : A, charac- 
 ter of the soil profile ; B, texture ; and C, modifying conditions. 
 
 Index numbers are used for each group of factors based on 100 per 
 cent expressing ideal conditions. 
 
 The characteristics listed under factor A, character of the soil pro- 
 file, are essentially those that determine the soil series. A grouping of 
 the soil series of California is given according to their position in the six 
 groups on the basis of factor A. Factors A and B together make up the 
 soil type. 
 
 Characteristics listed under factor C, modifying conditions, consist 
 of drainage conditions, alkali, etc. 
 
 The index is the product of the ratings given each of these three fac- 
 tors, A x B x C, the ratings and the final index being expressed in per- 
 centages. 
 
 By the use of this method of rating soils, a large number of divergent 
 types can be compared, or various tracts of land can be compared from 
 the soil standpoint. 
 
 The index for rating the agricultural value of soils presented in this 
 bulletin can be used as a basis for judging soils. 
 
 ACKNOWLEDGMENTS 
 
 The author wishes to acknowledge the assistance and advice of Pro- 
 fessor C. F. Shaw and Professor W. W. Weir in the preparation of this 
 paper. Helpful suggestions were also made by Mr. J. H. Keith, County 
 Assessor of Riverside County. 
 
40 University of California — Experiment Station 
 
 LIST OF SELECTED REFERENCES 
 
 For the information of those who wish to secure more specific soil data, the follow- 
 ing short list of books, bulletins, and circulars will be found to contain valuable 
 information. In addition to those listed below, many other good books and publica- 
 tions are available, but the publications listed below will be found of particular 
 use to those who do not find time for extended reading on this subject. Practical in- 
 formation on California soils can also be secured by consulting papers published in 
 the American Journal of Agronomy, Proceedings of the American Soil Survey Asso- 
 ciation, Soil Science, and other similar publications. 
 
 Emerson, Paul. 
 
 1930. Principles of soil technology, vii + 402 p. Macmillan and Company, New York. 
 Harris, F. T. 
 
 1920. Soil alkali, its origin, nature and treatment, vii 4- 258 p. John Wiley and Sons, 
 New York. 
 
 HlBBARD, P. L. 
 
 1931. Commercial fertilizers and soil fertility in California. California, Agr. Ext. 
 Cir. 57:1-37. 
 
 HlLGARD, E. W. 
 
 1912. Soils, iii 4- 593 p. Macmillan and Company, New York. 
 
 HOAGLAND, D. R. 
 
 1930. Fertilizer problems and analysis of soils in California. California Agr. Exp. 
 Sta. Cir. 317:1-16. 
 Powers, W. L., and T. A. H. Teeter. 
 
 1922. Land drainage, iii + 270 p. John Wiley and Sons, New York. 
 
 Robinson, G. W. 
 
 1932. Soils, their origin, constitution and classification. An introduction to ped- 
 ology, vii + 390 p. D. Van Nostrand Company, New York. 
 
 Shaw, C. F. 
 
 1927. Definition of terms in soil literature. Proc. 1st Intntl. Congr. Soil Sci. 4:38- 
 
 64. 
 1927. The basis of classification and key to the soils of California. Proc. 1st Intntl. 
 
 Congr. Soil Sci. 4:65-104. 
 1927. Profile development and the relationship of soils of California. Proc. 1st 
 Intntl. Congr. Soil Sci. 4:291-318. 
 United States Department of Agriculture. 
 
 Soil survey reports and maps (for the area in which the reader is interested.) 12 
 
 Weir, Walter W. 
 
 1932. Soil erosion in California: its prevention and control. California Agr. Exp. 
 Sta. Bui. 538:1-45. 
 
 12 See Appendix for soil surveys completed in California. 
 
Bul. 556] Index for Rating Value of Soils 41 
 
 APPENDIX : SOIL SURVEY DATA IN CALIFORNIA 
 
 There are two general types of soil surveys, the reconnoissance and 
 the detailed, that cover portions of California. The extent of these sur- 
 veys is shown on the map in figure 17. Reconnoissance surveys (shown 
 on the insert in fig. 17) are generalized soil surveys with maps made on 
 the scale of 1 inch to 2 miles or 1 inch to 4 miles. Seven such surveys were 
 made during the period between 1913 and 1917, covering the major por- 
 tion of southern California, the Sacramento and San Joaquin valleys, 
 and the San Francisco Bay region. These show the soils in rather in- 
 clusive groupings and rarely show bodies of soil less than 160 acres. 
 
 They are being supplanted as rapidly as facilities permit by detailed 
 soil surveys with maps made on the scale of 1 inch to 1 mile. On these 
 maps the bodies of soils as small as 5 or 10 acres in extent are shown. 
 All the soil maps are accompanied by reports giving a full description of 
 the soil types shown with a discussion of their geographical distribution, 
 relationship, and general utilization in that particular area. Where al- 
 kali is present to any extent a separate alkali map is published. In addi- 
 tion to the soil discussion, separate chapters are written covering the 
 general description of the area, the climate, the agriculture, and often 
 separate chapters on irrigation, drainage, and alkali conditions are in- 
 cluded. In recent publications, there is also a technical discussion of the 
 soils. 
 
 These soil surveys serve as an inventory of the soil resources of the 
 state and as a background for soil classification, soil evaluation, and 
 other studies. Before extensive studies can be made on individual soil 
 series or soil types, it is necessary to know in detail the characteristics of 
 these soils, and also the location, the general environment, and the ex- 
 tent of their occurrence. Basic studies on individual soil series or on 
 groups of soil series are now in progress and in due time this soil infor- 
 mation will become available in printed form. 
 
 Completed soil surveys available in printed form are listed in table 5, 
 those out of print in table 6, and those completed but not yet published 
 in table 7. 
 
ten/ '•"•vo U - 
 
 I — u_ W 
 
 7k*4* 
 
 
 
 
 
 "\r1 I 1 RE CONNOISSANCE 
 
 j / 1 AREAS 
 
 #j\ fTAINITr / 
 
 Ipsss-* 
 
 LPIKt) ^V 
 
 * — iMONO^k 
 
 UMNC \ > 
 
 
 \MeNoociNol 
 
 
 I \ ClCl 
 
 \ £?w V C0L 
 
 \I l3 I 
 
 iOLAljtt. 
 
 
 KB! 
 
 ^^C^f^; 
 
 
 
 
 
 
 -p N 
 
 
 vU& 
 
 
 
 
 
 
 
 @l 
 
 
 t& \ 
 
 ^"santaVarbari 
 
 1 *\ io 
 
 <4w> 
 
 
 
 
 
 
 25^ 
 
 4" 
 
 J||j 
 
 not ( 
 
 g IIP 
 
 Fig. 17. — Soil-survey areas in California shown by shading 
 
 1. Hanf ord 
 
 2. San Jose 
 
 3. Bakersfield 
 
 4. Sacramento 
 
 5. Stockton 
 
 6. Butte Valley 
 
 7. Colusa 
 
 8. Bedding 
 
 9. Modesto-Turlock 
 
 10. Pajaro Valley 
 
 11. Porterville 
 
 12. Marysville 
 
 13. Woodland 
 
 14. Livermore 
 
 15. Madera 
 
 16. Eed Bluff 
 
 17. Fresno 
 
 18. Merced 
 
 19. Ukiah 
 
 20. Healdsburg 
 
 21. Honey Lake 
 
 22. Pasadena 
 
 23. Eiverside 
 
 24. San Fernando 
 
 25. Anaheim 
 
 26. Los Angeles 
 
 27. Santa Maria 
 
 28. Ventura 
 
 29. El Centro 
 
 30. Grass Valley 
 
 31. Willits 
 
 32. Shasta Valley 
 
 33. Big Valley 
 
 34. Brawley 
 
 35. Eureka 
 
 36. Victorville 
 
 37. Lancaster 
 
 38. Palo Verde 
 
 39. Coachella Valley 
 
 40. Gilroy 
 
 41. Hollister 
 
 42. Auburn 
 
 43. Bishop 
 
 44. King City 
 
 45. Chico 
 
 46. Salinas 
 
 47. Oroville 
 
 48. Clear Lake 
 
 49. Placer ville 
 
 50. Santa Ynez 
 
 51. Paso Eobles 
 
 52. San Luis Obispo 
 
 53. Oceanside 
 
 54. Capistrano 
 
 55. ElCajon 
 
 56. Suisun 
 
 57. Dixon 
 
 58. Alturas 
 
 59. Lodi 
 
 60. Napa 
 
Bul. 556] 
 
 Index for Rating Value of Soils 
 
 43 
 
 TABLE 5 
 
 Soil Surveys Available in Pamphlet Form, 1932* 
 
 Number 
 as shown 
 on map 
 (fig. 17) 
 
 Area 
 
 Anaheim 
 
 Auburn 
 
 Big Valley 
 
 Bishop 
 
 Brawley 
 
 Chico 
 
 Clear Lake 
 
 Coachella Valley 
 
 El Centra 
 
 Eureka 
 
 Gilroy 
 
 Grass Valley 
 
 Hollister 
 
 Honey Lake 
 
 King City 
 
 Lancaster 
 
 Los Angeles 
 
 Lower San Joaquin Reconnois 
 
 sance 
 
 Middle San Joaquin Recon- 
 
 noissance 
 
 Date of 
 survey 
 
 1916 
 1923 
 1920 
 1924 
 1920 
 1925 
 1927 
 1923 
 1918 
 1921 
 1923 
 1918 
 1923 
 1915 
 1924 
 1922 
 1916 
 
 1915 
 
 1916 
 
 Number 
 as shown 
 on map 
 (fig. 17) 
 
 28 
 
 Area 
 
 Oroville 
 
 Palo Verde Valley 
 
 Pasadena 
 
 Placerville 
 
 Riverside 
 
 Salinas 
 
 San Diego Reconnoissance 
 
 San Fernando 
 
 San Francisco Bay Reconnois 
 
 sance 
 
 Santa Ynez 
 
 Santa Maria 
 
 Shasta Valley 
 
 Central-Southern California 
 
 Reconnoissance 
 
 Upper San Joaquin Reconnois 
 
 sance 
 
 Ventura 
 
 Victorville 
 
 Willits 
 
 Woodland 
 
 Date of 
 
 survey 
 
 1926 
 1922 
 1915 
 1926 
 1915 
 1925 
 1915 
 1915 
 
 1914 
 1927 
 1916 
 1919 
 
 1917 
 
 1917 
 1917 
 1921 
 1918 
 
 * Can be secured from the Division of Soil Technology, University of California, Berkeley, California. 
 
 TABLE 6 
 Soil Surveys No Longer Available for Free Distribution, 1932* 
 
 Number 
 as shown 
 on map 
 (fig. 17) 
 
 Area 
 
 Bakersfieldf 
 
 Butte Valley 
 
 Colusa 
 
 Fresnot 
 
 Fresnot 
 
 Hanfordt 
 
 Healdsburg 
 
 Imperialt 
 
 Imperial! 
 
 Indiof 
 
 Klamath Reclamation. 
 
 Livermore Valleyt 
 
 Los Angelest 
 
 Lower Salinas Valley ... 
 
 Maderat 
 
 Marysville 
 
 Mercedf 
 
 Date of 
 survey 
 
 1904 
 1907 
 1907 
 1900 
 1912 
 1901 
 1915 
 1901 
 1903 
 1903 
 1908 
 1910 
 1903 
 1901 
 1910 
 1909 
 1914 
 
 Number 
 as shown 
 on map 
 
 (fig. 17) 
 
 Area 
 
 Modesto-Turlockf 
 
 Pajaro Valley 
 
 Portervillet 
 
 Redding 
 
 Red Bluff 
 
 Sacramento 
 
 Sacramento Valley Reconnois 
 
 sance 
 
 San Bernardino t 
 
 San Gabriel t 
 
 San Josef 
 
 Santa Anaj 
 
 Stocktont 
 
 Ukiah 
 
 Venturaf 
 
 Yuma 
 
 Date of 
 survey 
 
 1908 
 1908 
 1908 
 1907 
 1910 
 1904 
 
 1913 
 1904 
 1901 
 1903 
 1900 
 1905 
 1914 
 1901 
 1904 
 
 * May be consulted at the principal public libraries in bound volumes of the Annual Field Operations 
 of the Bureau of Soils. 
 
 t Covered by more recent surveys. 
 
44 
 
 University of California — Experiment Station 
 
 TABLE 7 
 Soil Surveys Completed But Not Yet Published, 1932 
 
 Number 
 as shown 
 on map 
 (fig. 17) 
 
 Area 
 
 Date of 
 survey 
 
 Number 
 as shown 
 on map 
 (fig. 17) 
 
 Area 
 
 Date of 
 survey 
 
 51 
 
 
 1928 
 1928 
 1929 
 1929 
 1929 
 
 56 
 57 
 58 
 59 
 60 
 
 Suisun 
 
 1930 
 
 52 
 
 
 Dixon 
 
 1931 
 
 53 
 
 
 
 1931 
 
 54 
 
 
 
 1932 
 
 55 
 
 El Cajon 
 
 
 1932 
 
 
 
 
 
 13m-9,'33