This exhibition uses, as a point of departure, soil maps of Los Angeles County, which provide evidence of a great variety of human interventions in the landscape, such as landfills, new construction, mining, and agriculture.

The sites selected exemplify common soil interactions, in the margins of Los Angeles, and in other cities where development encroaches on virgin land. As we look at the utilization of soil for agriculture, mining and recreation, and the control of erosion necessary for the construction of Los Angeles’ ever expanding borders, we find that it is at these margins that the ground can be seen most clearly, before paving erases the layers of meaning that soil contains.

What are Soil Maps?

Soil maps are published by the Natural Resources Conservation Service, a division of the U.S. Department of Agriculture. They are aerial photographs with soil types superimposed, and they serve as general guides for a range of activities, from agriculture to mining and construction. While no substitute for the on-site investigation of a soil engineer, soil maps can provide an overview of large areas of land as well as features that may have been overlooked on U.S. Geographical Survey topographical maps.

Soil Map

In addition to describing natural features, soil maps provide a record of recent human interventions on the earth as well as a guideline for future land uses. The maps come with tables assessing the suitability of soil types for a variety of activities such as sand and gravel mining, septic tank filter fields, agriculture and excavation.

As Los Angeles has expanded, the margins have grown increasingly far from the center of the city, and the ground has disappeared beneath roads, parking lots and buildings. The last soil map produced by the Department of Agriculture for metropolitan Los Angeles, in 1916, describes the appropriateness level of all of the soils of the region for agriculture but notes that the increasing value of land will soon make agriculture unprofitable and general soil maps unnecessary. Agricultural use of the San Fernando Valley continued for longer, with the last soil map dating to 1969. With the decrease of agriculture in the region, the need for updating the maps has declined and the existing maps now provide a historical record, and an aerial photograph, of the past.

A History of Soil

What happens to any piece of land involves three factors: slope, the type of soil, and the economic value of the real estate. When real estate values rise, agricultural land is developed and steep slopes are graded and built out. On the edges of the vast suburbs of Los Angeles these “marginal” areas support a variety of land uses, agriculture, landfills, and off-road vehicle recreation.

For example, with rainfall concentrated in February and March, Southern California’s climate necessitates the construction of large flood control structures such as the Sepulveda Dam basin and the Santa Fe basin in Irwindale. These areas become sacrificial zones where construction is prohibited and the cataclysmic potential of flash floods can be contained. Aside from vacant lots and steep slopes, these flood control regions are some of the few undeveloped open spaces left in metropolitan Los Angeles.

Soil is malleable and can be excavated and mounded, built upon and abandoned, mined and amended. A deep gash becomes a landfill, a mountain is scraped for houses, a trench becomes a road, a deep shaft becomes a mine and the mine begets a mountain of tailings. Soil is a living fabric, an organic skin wrapping the earth’s stone and molten core; once disturbed it is never the same. Construction projects alter the soil as do the great earthquake faults of this region that lift, excavate, and transform.

Use it in place

Sod Farm
Agriculture in Los Angeles County accounts for just 5% of the total land in 1997 according to the U.S. Census bureau with most farm land in the Antelope Valley. Farm land has been steadily decreasing since 1900 when 34% of L.A. County was devoted to crops. The high value of real estate in metro areas has almost eliminated agriculture with the exception of a few plots of land in the San Fernando Valley. This Sod Farm near the corner of Balboa and Victory is owned by the Army Corp of Engineers and has been leased to Valley Sod Farms Inc. since 1986. No permanent structures are allowed since this area is part of the Sepulveda flood control basin. Before its incarnation as a Sod Farm it was a corn field.

Vacant Lot
There is nothing extraordinary about this vacant lot near the corner of Owensmouth and Nordoff in Chatsworth. The soil maps described this particular soil as being ideal for construction, “It is free of stones and is not limited by depth to bedrock or to a high water table. Trenching and grading can be done by standard procedures. The San Emigdio soil is relatively low in content of clay and organic matter. It has low shrink-swell potential.” The fate of this lot is shaped not by geological factors but by economic forces, and while at one time agricultural, this lot like most land around it will eventually be developed.

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Off-Road Vehicle Recreation
Steep slopes often make land less desirable for building or agriculture, but are an asset when it comes to off-highway vehicle (OHV) recreation. In an attempt to limit unofficial OHV areas spreading on the margins of cities, the State of California has established the Hungry Valley State Vehicular Recreation Area and six other OHV parks scattered throughout the state. Four thousand acres of Hungry Valley, located just west of Gorman, are set aside for open riding with a variety of trails graded according to difficulty, a practice mini-track and a motocross track. The more difficult trails with steep grades and blind drop-offs provide both a challenge and danger as seen in this section of trail, the scene of an accident under investigation. OHV accidents are common occurrences, and considerable debate exists over the impact of dirt bikes and ATVs on soil erosion and compaction. Like the dam basins sacrificed to occasional flooding, these recreational zones are sacrificed to a controversial pastime.

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Trenching
Trenching, being done here in the construction of a pipeline, entails considerable risks to workers operating at the bottom of the pit. Cave-ins can be caused by rain, nearby building foundations, and vibrations caused by heavy equipment. The large metal structure surrounding the pipeline in this photo is a shoring cage designed to withstand soil pressures and prevent cave-ins. Shoring cages are dragged or dropped into place and can even be stacked. Soil types must be taken into account when excavating because certain soils require more shoring than others.

Drainage Slope
Two methods of erosion control are visible on this hillside in the new Westridge Estates development on land owned by the Newhall Land and Farm Company in Valencia. Hydroseeding, a method of spraying a green tinted slurry of seeds and fertilizer over a large area to reestablish vegetation is applied after hillsides have been cleared and graded. Paved interceptor ditches directed towards a drain consolidate runoff and prevent erosion.

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Winter Rains
Before the drainage control infrastructure is fully in place, cataclysmic winter rains can create chaos in a new building site. Seen here in the Westridge Estates development in Valencia, sandbags have been placed as a temporary measure to re-direct water during heavy March rains.

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Quarry
This gravel quarry is part of a series of pits located in the Little Rock wash in the Antelope Valley. Gravel, already ground by the forces of erosion, is excavated here and in surrounding pits, producing the aggregate that has built the roads and structures of this rapidly growing desert community.

Concrete pour
Cement, made by heating limestone in a kiln, is an ingredient of concrete, which is produced by mixing air, water, aggregate and cement. Varying the mix of these ingredients changes the strength and uses of concrete. Concrete plants are often located near the quarries that produce the aggregate, and once activated with water concrete must be either used or disposed of. In this image, taken in the Antelope Valley, excess concrete has been dumped over the side of the pit - a new, man-made rock, cascading back into the source of its ingredients.

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Asphalt
Asphalt is another product that depends on aggregate for its production. It is made up of 95% stone, sand, or gravel, bound together with asphalt cement, which is a product of petro-chemical production. Asphalt offers a smoother and quieter ride than concrete roads, and 94% of U.S. roads are paved with asphalt, including 65% of the Interstate Highway system. Asphalt is also used as a pond and reservoir liner – the Metropolitan Water District of Southern California has used it for this purpose for over forty years. Asphalt is fully recyclable and can be picked up and reused. Asphalt cement is heated and mixed with aggregate, placed in trucks and taken to the paving site. The asphalt is applied by hoppers in front of the paving machines and compacted by heavy rollers. Traffic can drive over the new surface within minutes. In this image surplus asphalt has been dumped by the side of the job site atop a common soil of the Antelope Valley classified as “Pond-Oban Complex”.

Soil Maps and Data:
United States Department of Agriculture Soil Conservation Service In Cooperation with University of California Agricultural Experiment Station, Soil Survey Antelope Valley Area (January 1970).

United States Department of Agriculture Soil Conservation Service and West Los Angeles County Resource Conservation District in Cooperation with University of California Agricultural Experiment Station, Soil Survey of Los Angeles County, California, West San Fernando Valley Area (January 1980).

United States Department of Agriculture Natural Resources Conservation Service, Report and General Soil Map Los Angeles County California (December 1969).

RESEARCH + Production:
Erik Knutzen, Matthew Coolidge, Steve Rowell, Sarah Simons.

Special Thanks To:
Antelope Valley Resource Conservation District, Los Angeles Public Library, Mike Jacobson, Eric Vinson at the National Soil Survey Center, John Weldon.

This exhibition was made possible in part by a grant from the City of Los Angeles Cultural Affairs Department.