What is the California state soil?

As you know, many states have a designated state bird, flower, fish, tree, rock, etc. And, many states also have a state soil – one that has significance or is important to the state. We’ve previously written about New Jersey’s state soil, Downer. The San Joaquin is the official state soil of California.  Let’s explore how the San Joaquin is important to California and even the entire world.

California chose San Joaquin as the state soil because of it has:

  1. interesting soil characteristics;
  2. agricultural significance;
  3. extensive distribution;
  4. a name recognizable as Californian; and,
  5. a typical location in California.
Map showing red dots that signify the location of the San Joaquin soil in California
Distribution of San Joaquin soil in the state of California starts north of Sacramento and extends to south of Fresno. Credit: Topographic image courtesy of National Geographic Society, 2013.

The gross value of agricultural production in the San Joaquin Valley of California exceeded 39 billion dollars in 2014. San Joaquin soils occupy a niche along the east side of the San Joaquin and lower Sacramento Valleys. They are a small but important part of this huge California agricultural base. San Joaquin soil is not the best soil for production of crops. However, with proper management, this soil has produced many billions of dollars of agricultural wealth for the state’s economy.

Uses of the San Joaquin

In general, most soils can be used for agriculture (growing foods, raising animals, stables); engineering (roads, buildings, tunnels); ecology (wildlife habitat, wetlands), recreation (ball field, playground, camp areas) and more.

Originally, this soil was used for livestock grazing and wildlife habitat. San Joaquin soils today also support growth of an abundant variety of irrigated crops including almonds, pistachios, figs, grapes, oranges and wheat. Knowledge of the San Joaquin soil’s properties and characteristics has become increasingly important in suburban and urban development. Population centers such as the city of Fresno have expanded into areas of San Joaquin soil.


San Joaquin soil has limitations for irrigated crops and septic tank absorption fields. San Joaquin has a hard layer below the surface – the depth of this hard depends on location. This abrupt, hard, layer restricts rooting depth and water penetration. Therefore, irrigated crops (particularly fruit and nut crops) are limited by this rooting depth and restricted water penetration. Septic tank absorption fields are limited by the very slow rate at which water moves through the soil.

Besides its agricultural limitations, San Joaquin may pose engineering problems for house construction.  If the hard layers are not removed or otherwise well drained, landscape irrigation water may “perch” the top layer. This could cause seasonal expansion and contraction of the soil. This, in turn, could potentially damage buildings, as well as locally contributing to formation of mold.

San Joaquin soils can form “hog wallows.” This creates an undulating landscape with depressions that fill with water, called ponding. Credit: Phil Smith, USDA-NRCS

Where is San Joaquin found in California?

The San Joaquin soil occurs on a geologic formation known as the “Riverbank.” The upper part of the Riverbank was probably laid down during a major glacial event in the Sierra Nevada. The San Joaquin soil formed mainly during the following interglacial epoch of relative geomorphic (landscape) stability.

Very blue sky with few clouds, a line of grass and trees, then marshy, watery area with some grasses in foreground reflecting the blue of the sky
Vernal pools like this one in Santa Rosa Plateau, CA, appear seasonally. The winter of 2019 had particularly good rainfall (and mountain snow) in California, so this pool filled well in April, 2019. Vernal pools were once common in the region of San Joaquin soils which are now used to grow food. Credit: Susan V. Fisk

The region lies in flat valley basins of deep sediments adjacent to the Sacramento and San Joaquin Rivers, as well as the fans and terraces around the edge of the valley. The two major rivers flow from opposite ends of the Central California Valley, entering the Sacramento–San Joaquin River Delta and San Pablo Bay. The region once contained extensive prairies, oak savannas, desert grasslands in the south, riparian woodlands, freshwater marshes, and vernal pools. More than one-half of the region is now in cropland, about three-fourths of which is irrigated. Environmental concerns in the region include salinity, ground water overdraft, and subsidence, loss of wildlife and flora habitats, and urban sprawl.

Fun fact

A fun fact about San Joaquin soils is that they can form “hog wallows.” This creates an undulating landscape with depressions that fill with water, called ponding.

To download the entire San Joaquin Series – California State Soil booklet, or to see any of the other state booklets already completed, visit http://www.soils4teachers.org/state-soils

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