SOIL GENESIS AND MORPHOLOGY OF A MONTANE MEADOW IN THE NORTHERN SIERRA-NEVADA RANGE

Given the importance of riparian areas in the western United States, k nowledge about the spatial distribution, properties, and genesis of th ese soils is surprisingly limited. In conjunction with an interdiscipl inary study of the impacts of grazing on soils and vegetation, we Char acterized three pedons along a hydrologic gradient on a montane meadow of the northern Sierra Nevada range. Radiocarbon dating of charcoal i ndicates that meadow pedogenesis began approximately 3600 years B.P., after a catastrophic valley erosional event. Since that time, nearly 1 meter of soil has accumulated over a basal glaciolacustrine unit. Cri tical factors and processes influencing soil genesis and morphology in clude: seasonal variation in soil redox status, frigid soil temperatur es, additions of volcanic tephra, wildfires, and polygenesis related t o Holocene climatic, hydrologic, and vegetation changes. Argillans are present on ped faces of certain soil horizons, which suggests extende d dry periods at which time clay pervection occurred. Clay mineralogy is disjunct; surface horizons are dominated by kaolinite and underlyin g horizons by smectite. The high clay content of such youthful soils s uggests rapid primary mineral weathering. Charcoal-containing strata a ttest to frequent wildfires during the Holocene epoch. The spatial com plexity of soil patterns and their properties infers that these ripari an areas are dynamic, and their character may have been shaped by prev ious climatic patterns.