Soil mineralogy trends in California landscapes

Californiaʹs diverse environmental gradients serve as natural experiments for examining controls on soil mineral distribution in landscapes. In this paper we use example soilscapes from throughout California to examine how lithology, climate, topography, and duration of pedogenesis interact to produce distinctive weathering environments and characteristic suites of soil minerals. Seven soil-geomorphic sequences were assembled from the literature to illustrate major soil mineralogical trends: 1) granitic terrain of the Peninsular Ranges, 2) granitic terrain of the central Sierra Nevada, 3) andesitic terrain of the northern Sierra Nevada, 4) fluvial terraces on the east side of the Great Valley, 5) marine terraces of the central coast, 6) ultramafic terrain of the Klamath Mountains, and 7) an alluvial fan in the Mojave Desert. Results of this analysis show that kaolin is present in virtually all pedons, irrespective of climate, parent material, age, or topographic position. Kaolin does not form in ultramafic soils due to insufficient aluminum. Many secondary clay minerals reflect the stateʹs strong climatic influence, with palygorskite, smectite, and vermiculite in the dry, hot environments; hydroxy-interlayered minerals, gibbsite, and short range-ordered minerals in the cool, moist environments. In arid and semi-arid regions, the distribution of calcite, gypsum, and soluble salts is strongly related to patterns of eolian dust deposition and water infiltration and leaching.