The Historical Maps From The Wine History Project Collection Document The Soil In SLO County In 1928

A coordinated effort of national soil mapping began in the United States in 1899. It began with a nationwide partnership of federal, regional, state, and local agencies, private entities, and universities. This idea of a soil survey in our country, some say originated with Milton Whitney, a professor of geology and soil physics at the Maryland Agricultural College and a physicist at the Experiment Station. He published a paper in 1892, “Some Physical Properties of Soils in Relation to Moisture and Crop Distribution” in which he examined a number of soils. That paper showed that agricultural properties are closely related to the texture of the soil and that the physical properties determine the yield of the crops. A new school of thought relating to the processes of plant nutrition led to the development of the Soil Survey. The leader of this new school was Milton Whitney.

The National Cooperative Soil Survey was established in 1899 and included work in multiple parts of the country. It was national in the sense that it was standardized and overseen at the national level. These first soil surveys were focused on the tobacco lands of Cecil County, Maryland and Connecticut Valley, Connecticut. The areas mapped were usually counties or topographic features. To keep the mapping effort moving, soil survey crews typically worked in northern locations during the summer months and southern locations through the winter months.

Who Is Milton Whitney? (1860-1927)

Milton was partly a physicist by training, and he applied that physics knowledge to the physical characteristics of soils. After some preliminary investigations of soils in Maryland, Whitney developed a theory that related soil fertility, and hence crop adaptability primarily to physical rather than chemical soil conditions. He considered that crop adaptability and production were controlled essentially by moisture relations. The most significant characteristics in the soil being analyzed were thought to be associated with the size of the pores. Therefore the texture of the soil was most important.  

The Soil Survey under Milton Whitney, for all its shortcomings, consistently recognized and mapped soils in terms of one specific soil characteristic – soil texture. Once the importance of soil texture was established, the approach to future Soil Surveys changed. Many characteristics were defined so that future mapping expanded the research and interpretation and that continues in the present day. 

As Chief of Bureau of Soils beginning in 1894 and ending with his death in 1927, Whitney oversaw geography and chemistry-based surveys designed to understand, manage, conserve and sustain the nation’s soil resources.

Delegates Represent The Association of American Agricultural Colleges and Experimental Stations in 1891

In Washington, D.C. in August of 1891 delegates from the states and territories met for the fifth annual convention of the Association of American Agricultural Colleges and Experiment Stations. Some delegates urged for the establishment of official weather observation stations at each state experiment station. The resolution from this was: “…the Bureau should organize and assist in maintaining a study of climatology in its relations to farming, in cooperation with the colleges and stations and that the sphere of this work should be enlarged to include the physics, conditions, and changes of agricultural soils.”

On February 14, 1894, Assistant Secretary of Agriculture, C.W. Dabney recommended to the Secretary of Agriculture, J. Sterling Morton, that a division be established and on March 3, 1894, Milton Whitney was named Chief of the Division of Agricultural Soils. This new Division was established within the Weather Bureau which clearly broadened the understanding of climate as a complex set of factors, including weather. 

But by October 1894 the Division was established as an independent division in agriculture (effective July 1895). The Agriculture Appropriation Act for 1896 designated the Division of Agricultural Soils and appropriated $15,000 for staff and research. By the time the Appropriation Act for 1897 was in effect, the unit became known as the Division of Soils. This Division of Soils became better known as the National Cooperative Soil Survey in May 1899. By year end the area mapped totaled 720,000 acres of four separate soil surveys. They were:

• Pecos Valley, New Mexico
• Salt Lake Valley, Utah
• Connecticut Valley, Connecticut and Massachusetts
• Cecil County, Maryland

A reorganization was approved by both Houses of Congress and signed by President McKinley on March 2, 1901. The newly created Bureau of Soils was granted an appropriation of $109,140 for the fiscal year 1902.

1920-1933 Soil Mapping

In the 1920s the art of aerial photography improved dramatically. State soil survey leaders incorporated this new technology. 

According to David Rice Gardner’s thesis, page 104, a member of the American Soil Survey Association commented in 1928: “We are not so much a Survey Association, as a Soil Association, or a Soil Science Society.” Until 1930, the soil type was the most common mapping unit. 

Another important improvement during this period was an increase in the scale of field maps. With the increase in field scale came a higher degree of cartographic accuracy by the soil surveyors. As a result, many of the men of the Soil Survey became highly skilled field cartographers and draftsmen. Soil survey maps became more accurate each year. This technology improved the mapping of local and county roads in each area. 

The cost of field mapping was estimated about one cent per acre in 1929. Soil surveyors covered the area to be mapped by hiking; the average coverage per man per day was about two square miles.

As mentioned previously aerial photography became part of the process in mapping. In 1929 and 1930 the first county soil survey in the United States made entirely on large scale air photo base maps was completed in Indiana for Jennings County.

By 1930 the American Soil Survey Association went on record with the following resolution:

WHEREAS: aerial photography has proved very useful as an aid in soil mapping, Be It Resolved that this Association urges the cooperation of the Federal and State Soil Surveys with other organizations interested in the use of aerial photographs, with the view of affording mutual assistance and of reducing the cost of such work.

The Soil Survey was created at the same time as the soil mapping was done. The Wine History of San Luis Obispo County does not have a copy of this survey within our collection, but we do have copies of the two soil maps that were published at that time.

Henry G. Knight was the Chief of the Bureau of Chemistry and Soils at the time this pamphlet was published and the Chief of Soils Investigations was A.G. McCall. According to the acknowledgements within the document, this was in cooperation with the University of California Agricultural Experiment Station.

 The Directory of that organization at the time was E.D. Merrill and Charles F. Shaw were in charge of the Soil Survey.

The report described in detail the soils of the San Luis Obispo area and discussed their agricultural adaptations. The soil maps which accompanied this report described their acreage and proportionate extent. The following shows the table created with this information which appeared in this pamphlet.

Table 3 which was included in the Soil Survey of the San Luis Obispo Area
By E.J. Carpenter, U.S. Department of Agriculture, in charge and R. Earl Storie, University of California, 1928

The Soil Maps in the Wine History Project of San Luis Obispo County Collection

EPH255
San Luis Obispo County Soil Maps
North (left image) and South (right image)

No census data covering only the area surveyed on these two maps was available. Figures given for the county were used and according to the census for 1930 San Luis Obispo County had a population of 29,613 of which 63.4% was classed as rural. The rural population included persons living in towns of less that 2,500 inhabitants and had a density of 5.6 persons a square mile.

The greater proportion of the foreign-born whites came largely from southern Switzerland and had the customs and language of the Italian population living in the area surveyed and were engaged largely in the dairy industry. A small percentage of Indigenous Americans, Chinese, Japanese and African Americans lived in the county. Many of the Japanese were engaged in vegetable gardening south of San Luis Obispo. Most of the Chinese and African Americans lived in the towns. 

The principal town of the area in 1928 was San Luis Obispo with a population of 8,276 according to the same 1930 census and served as a shipping point for cattle, grain, and dairy products.

The Wine History Project of San Luis Obispo County obtained these two maps from Jim McCormick of the California Wine Museum collection. His personal wine museum collection has been online as a “virtual museum” since 2008. These soil maps are artifacts which are now a part of our artifacts and archives as they have great importance to San Luis Obispo’s wine history.

These maps include the following table detailing the color coding for the types of soils found in the soil mapping process used in 1928.

Who Uses Soil Maps?

While early soil surveys were made to help farmers locate soils responsive to different management practices and to help them decide what crops and management practices were most suitable for the kinds of soil on their farms, the use of these documents keeps widening. 

The soil survey and the maps included are used by the scientific community, the public, farmers, ranchers for soil management.  They also assist land managers in developing strategies for soil conservation and restoration. These same maps are used by engineers and construction professionals to design buildings, roads, and other infrastructure projects. 

Viticulture Use of Soil Maps for San Luis Obispo County 

A 1928 soil survey map, most probably the north map shown earlier in this article which mapped the area of Paso Robles, was utilized for the petition for the proposed expansion of the Paso Robles AVA in 2008. By including the 1928 soil map along with the upgraded maps from the 1970s and 1990s the federal government could look at topography, climate, soils, geologic history, and geomorphology. This information was sent to the Department of the Treasury, Alcohol and Tobacco Tax and Trade Bureau to expand by 2,635 acres the existing 609,673-acre Paso Robles American viticultural area in San Luis Obispo County, California. 

With approval of this expansion the Central Coast viticultural area allowed vintners to better describe the origin of their wines and to allow consumers to better identify wines they may purchase.

Conclusion

Remember in the early years, the vision of the efforts was that the soil survey combined geography with soil chemistry. The men conducting the surveys were geologists or chemists and none had training in agronomy. Soil texture was the main differentiating soil characteristic. Eventually characteristics were added which included organic content, soil structure, soil color, erodibility, drainage, and nature of subsoil. 

The land-grant universities from the very start were close partners in the National Cooperative Soil Survey. By 1920, most soil surveyors were graduates of land-grant universities and other agricultural colleges with training in soils and crops.  Between 1899 and the 1950s both state and federal agencies had financial support to perform soil survey work. 

The Federal leadership in the National Cooperative Soil Survey partnership including all mapping, classification, interpretation, laboratory services, map compilation and nationwide publication was given to the Soil Conservation Service (SCS) which Franklin D. Roosevelt had originally created it in 1933 under the Department of the Interior. There was a consolidation of soil survey activities during the Eisenhower administration of the 1950s.

Soil maps for San Luis Obispo County have been created and updated since these original maps from 1928 and can now be located on the internet. https://www.arcgis.com/apps/Legend/main/index.html?appid=3ec23cfdbb74495fb2e31e96d1359b6f