Soils of the Prime Desert Woodland Preserve

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By Russell Almaraz

The desert soils which occur at the Prime Desert Woodland Preserve were formed, over many millennia, from granitic stream deposits originating from the nearby San Gabriel Mountains. The tributary waters of Amargosa Creek transported the sands, silts, and clays from the mountains, and layered the deposits on the valley floor. Over time, these deposits accumulated and became very deep over the bedrock. Distinctive plant communities colonized these soils and unique species occasionally evolved. Each soil type developed distinguishing features from the affects of climate, parent material, organisms, and time.

The soil quality of the first 5 feet is vital to plant growth and to most of the land uses that soils are managed for. The soil’s differential reaction to rain and temperature causes soil decomposition or “weathering” to occur. These processes form the characteristic features of different soil types. Soils are classified by soil scientists according to a hierarchal classification, or taxonomy, similar to the system used for classifying plants and animals. A soil series name is also given. The soils of the Prime Desert Woodland Preserve were mapped by soil scientists of USDA’s Natural Resources Conservation Service in the mid-1960s, and published in the Antelope Valley Soil Survey Report.

Joshua TreesThe soils of the Joshua Tree–Juniper Woodland vegetation community, along the North Trail complex, are named the Sunrise Series. These sandy soils occur on an old undulating dune landscape molded by wind. These dunes are stabilized, from further wind erosion, by thick stands of Joshua Trees and California Juniper. Underlying most of these soils is a hard cement-like layer, called caliche, which resulted from rain-leached accumulations of calcareous minerals. The upper surface of the caliche layer can be viewed from the bridge on Joshua Tree Trail, where the stream cut through the soil surface layer and exposed the caliche. The hard caliche layer tends to hold rain water near the surface, accessible to plant roots, thereby supporting a dense plant community.

The soils of the Desert Scrub vegetation community, along the South Trail complex, are named the Cajon and Adelanto Series. These relatively young sandy loam soils occur on a nearly level landscape. They have a sandy subsoil and lack a caliche layer. Because a caliche layer is not present, rain water is quickly moved down through the soil and out of the reach of plant roots. These soils dry quickly, thus cannot support the dense vegetation of the Sunrise Series. The vegetation is more widely spaced and consists of some different species of plants which characterize the Desert Scrub community. Joshua Trees and California Junipers occur more scattered here.

The soil should be considered along with the Preserve’s plants and animals, as an inseparable part of nature’s ecosystem. Its life supporting role for both flora and fauna provides the stage floor for the grand presentation of nature’s show.