AN INFORMATIVE LEGEND FOR SOIL MAPS

byCHAS. F. SHAW,

University of California, Berkeley, California.

The legends of the soil maps, with their blocks ofcolor and symbols arranged in alphabetical order, areconvenient if one is looking for the name of the yellowmarked Al, or the blue area labelled Zc, or if one wishesto locate areas of Aiken loam or Zaca clay. They may bemade very much more expressive, and made to carrymuch additional information by adding a few interpre-tive lines and by rearranging the blocks of color in con-formity to simple classification schemes.

To illustrate the possibilities of this arrangement,a new legend is submitted for the Auburn Area, C-ilifor-nia, and the Chico Area, California. These legends, givenhere in tabular form, would with their blocks of color,occupy but little more space on the map sheet than didthe original legends, and would carry much more infor-mation regarding the soils of the area.

The most inclusive categories place the soils in twogroups—the Primary soils formed by residual weather-ing from hard rocks, the Secondary soils formed byweathering from unconsolidated materials that have beentransported and deposited by water as alluvial fans andbroad alluvial plains.

Each of these categories is again divided on thebasis of degree of leaching and character of weathering,where the latter is known. Both non-calcareous and cal-careous soils, or Pedalfers and Pedocals, occur in eacharea, and some of the soils show definite trend in weath-ering that can be recognized as latoritic in character.Surveys in other regions would show similar trends thatmight be podzolic or chernozemic, or mi^ht fit into someother "climatic" class that can be indicated. If theweathering trend is not positively in evidence, as is thecase with some soils in these areas, this subclass designa-tion can be omitted.

SOIL MAP OF AUBURN AREA

L E G E N DPrimary Soils

Pedalfers - Lateritic

Granitic MaterialSemimature profile

Sierra loamImmature profile

Holland sandy loamHolland sandy loam (rock outcrop phase)Siskiyou course sandy loam

Sandstone and Shale MaterialImmature profile

Sites stony loom

Basic Igneous MaterialSemimature profile

Aiken clay loamAiken clay loam (shallow phase)Aiken clay loam (yellowish-subsoil phase)Aiken stony clay loam

Tuffaceous Sandstone Material(probably not lateritic)Immature profile

Whitney fine sandy loam

Secondary Soils

Pedalfers - Lateritic

Granitic Material

Recent AlluviumHanford sandy loam

Semimature profilePlacentia sandy loamPlacentia sandy loam (brown phase)

Mature profileSan Joaquin gravelly loamSan Joaquin fine sandy loamSan Joaquin loamJMadera loamRocklyn fine sandy loamRocklyn fine sandy loam (brown phase)Rocklyn fine sandy loam (gravelly phase)Alamo clay

Basic Igneous MaterialRecent Alluvium

Honcut clay loamHoncut clay loam (yellow-subsoil phase)

Semimature profileTuscan stony loam

Mixed MaterialRecent Alluvium

Columbia fine sandy loamColumbia fine sandy loam (coarse-textured

phase)Columbia fine sandy loam (shallow phase)Columbia silt loam

Immature profileCorning gravelly loamKimball loam

Pedocal - Rendzinas (probably)

Basic Igneous MaterialImmature profile

Hovey clay

Miscellaneous

Placer DiggingsRiverwashRough stony landScablandRough mountainous land

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SOIL MAP OF CHICO AREA

L E G E N D

Primary Soils

Pedalfers - Lateritic

Basic Igneous MaterialSemimature profile

Aiken clay loamAiken clay loam (stony phase)

Sandstone and Shale MaterialImmature profile

Sites fine sandy loam

Pedalfer*

Sandstone and Shale MaterialSemimature profile

Mariposa stony loam

Tuffaceous Sandstone MaterialImmature profile

Pentz clay loamPentz clay adobe

Secondary Soils

Pedalfers - Lateritic

Basic Igneous MaterialRecent Alluvium

Honcut sandy loamImmature profile

Reefers gravelly loamReefers gravelly loam (stony phase)

Semimature profileAnita clay loamAnita clay loam (reddish phase)Anita clay adobeAnita clay adobe (overwash phase)Tuscan stony clay loamTuscan gravelly clay loam

Mixed MaterialRecent Alluvium

Columbia very fine sandy loamColumbia loamColumbia loam (shallow phase)Ramada slit loam

Immature profileCorning gravelly sandy loam

Mature profileRedding clay loamRedding clay loam (gravelly phase)

Granitic MaterialMature profile

San Joaquin sandy loam

Pedocals

Basic Igneous MaterialRecent Alluvium(not now calcareous but evidently weatheringto pedocals)

Vina fine sandy loamVina fine sandy loam (shallow phase)Vina stony loamVina loamVina loam (shallow phase)Vina loam (gray phase)Vina clay loamVina clay adobe

(Calcareous subsoils)Conejo loamConejo clay loamConejo clay loam (heavy-textured phase)

Youthful profileFarwell fine sandy loamFarwell loamFarwell clay loamFarwell clay adobeNord fine sandy loamNord loam

Mixed MaterialImmature profile

Sacramento claySemimature profile

Stockton clay adobeStockton clay adobe (brown phase)Stockton clay adobe (overwash phase)Landlow clay loamLandlow clayLandlow clay adobe

Miscellaneous

Rough broken and stony landScablandRiverwashTailings

These broad climatic classes are subdivided on thebasis of the mineralogical character of the parent mater-ial, most easily expressed as origin from a kind of rock,as from Granitic Material, or from Basic Igneous Mater-ial, or from Sandstone and Shale Material, etc. Suchdivisions carry considerable indirect information regard-ing the probable chemical composition and physical char-acter of the soil, and by reason of the general under-standing of these geological terms, aid materially in in-dicating the characteristics of the soil.

These divisions are subdivided into stages of weather-ing or age groups in which the soils are arranged inorder as Recent or Recent Alluvium, Young, Immature,Semimature, and Mature. These stages carry to the userof the map much information regarding profile character-istics particularly with reference to the subsoil condi-tions, the degree of eluviation of A horizon, and ofilluviation and of induration in the B horizons.

We are not making any further subdivisions, oradding any descriptive subscripts, feeling that thesemight make the legends too involved. Further, it is oftenimpossible to carry in a few words, sufficient informa-tion to properly distinguish the soils, and a brief inade-quate statement description might be Inisleading. Insome areas, with few types and simple conditions, suchadditional information might be added in the form ofsubscripts, indicating the general color of the soil andsubsoil and possibly other distinguishing characteristics.

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The preparation of this type of legend requiressome additional work by the field men, both in deter-mining the relationship of the several soil series, andin the mechanical set-up of the legend arrangement. Itwill also demand attention from the inspectors afterlaboratory work and correlation are completed, in re-arranging the legend as necessitated by the additionalinformation on the character of the soils, and 'by thechanges in correlation. In most cases, this work wouldbe relatively simple and easy.

With the general scheme as set forth above, modi-fied and adapted to fit the local conditions of each area,the soil maps could be read very much quicker and wouldcarry much more information to the user. Our soil sur-vey is frequently criticized by foreign pedologists, whoallege that there is a lack of system, and a confusing

multiplicity of soil types and of soil series. Some haveinsisted that we have no classification and even fail tounderstand that the soil series within the United Statesare correlated, or that the soil series and soil type arespecific entities. Much of the criticism of our maps wouldbe overcome by this simple and inexpensive rearrange-ment of the Genetic and generic relationships ofseries would become at once apparent to the trainedsoil scientist who knew the fundamentals of soil taxo-nomy. The text of the report would still be the heart ofthe survey and would in no way be supplanted. Instead,it would be strengthened by the concise and graphic ex-pression of soil relationship presented by the legend onthe map. The more informative legend is presented as ameans of improving the usefulness of the soil surveysto both the layman and to the scientist.

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