Soil geomorphology of the north flank of the San Bernardino Mountains, California

There have been few soil geomorphology studies that have evaluated the combined influences of multiple soil forming factors on soil landscape evolution. The granite- and limestone-dominated north flank of the San Bernardino Mountains, southern California is an excellent study area in which to evaluate soil landscape evolution as a function of climate, tectonics and rock type because of the well-documented Quaternary tectonic and climatic history of the range. Approximately 40 soils were examined along the north flank piedmont on alluvial fans that range in age from Middle Pleistocene to latest Holocene and that range in composition from primarily carbonate rock types to primarily granite rock types. Field and laboratory investigations revealed that soil development is strongly controlled by sediment composition. Carbonate-dominated alluvial fans are characterized by soils with strong petrocalcic horizon development. Granite-dominated alluvial fans are characterized by soils with argillic horizons and little accumulation of pedogenic carbonate.; Sediment-composition-related soil development significantly influences geomorphic processes and the overall landscape evolution of the San Bernardino piedmont. Soils with rock like petrocalcic horizons are resistant to erosion. When tectonic folding deforms these soils, prominent anticlinal ridges form and episodically dam and/or reroute drainages along the mountain front. The location of these ridges largely controls the spatial and stratigraphic distribution of sediments in limestone-dominated portions of the piedmont. Argillic horizons in granite-derived deposits produce significant runoff and are easily eroded. Folds forming in these deposits are thus topographically less pronounced than folds forming in the limestone-dominated piedmont. Older deposits with argillic soils are often eroded and reworked and incorporated into younger deposits on the piedmont. In addition, drainage basins that are underlain by preweathered granite bedrock are sensitive to climate change. The stratigraphy of alluvial fans adjacent to these basins is therefore dominated by Holocene sediment.; Overall soil variability along the north flank of the San Bernardino Mountains strongly reflects interactions and feedbacks at different temporal and spatial scales between climate, tectonics, geomorphology and soil development itself. An accurate interpretation of the Quaternary history of this landscape is dependent on understanding both soil and geomorphic relationships across the San Bernardino piedmont.