Soil properties of selected pedons on ultramafic rocks in Klamath Mountains, Oregon

Ultramafic (serpentinized) rocks are parent materials for some soils in the Klamath Mountains in southwestern Oregon. Two map units in Curry County Soil Survey (e.g., Serpentano and Snowcamp) have typical vegetation and characteristics of serpentine soils, with low productivity and sparse stands of trees and slope stability problems related to the highly faulted and sheared bedrock. Using standard methods for x-ray diffraction (XRD) and optical analysis, representative pedons selected from Serpentano and Snowcamp map units were not initially classified into the U.S. Soil Taxonomy as magnesic (soil mineralogy dominated by magnesium-silicate minerals). This inconsistency between field observations and laboratory data initiated our investigation. We subsequently examined other laboratory properties and developed alternative quantification procedures that may be useful in classification of these soils. In this study, some distinguishable chemical properties of serpentine soils are low extractable calcium/magnesium (Ca/Mg) ratios (generally < 1.0 in both Serpentano and Snowcamp) and relatively higher Fe(2)O(3), MgO, nickel (Ni), chromium (Cr), cobalt (Co), and lower SiO(2), Al(2)O(3), CaO. Na(2)O, K(2)O than typically found in non-mafic rocks. Amounts of serpentine (quantitative) were quantified by two different laboratory methods (total analysis and thermogravimetric analysis, TGA). These data confirm initial field observations and soil mapping that Snowcamp classifies as clayey-skeletal, magnesic, frigid Andic Hapudalfs, whereas Serpentano fails the taxonomic criteria for magnesic mineralogy and classifies as clayey-skeletal, isotic, mesic Andic Eutrudepts.