Spodosol-Inceptisol Transition along an Elevation Gradient in the Klamath Mountains, Northern California

In western North America, Spodosols are relatively abundant in the Cascade Range and along the Pacific Coast as far south as the northern border of California. Fewer than 240 ha of Spodosols are mapped in California (along the north coast), but conditions favorable for their formation exist at some high-elevation sites in northern California, and some of the soils there have morphologies suggestive of Spodosols. This investigation sought to determine if these soils are Spodosols and, if so, to better understand the properties and genesis of soils at the margin of the Spodosol environment. Four pedons were sampled along an elevational transect (1817–2036 m) on a late Pleistocene ground moraine in the Klamath Mountains. The two highest-elevation pedons have E horizons depleted of organic C and organically bound Fe and Al, and underlying Bs horizons in which these compounds are concentrated. Below 1950-m elevation, the soils transition to having A and Bw horizons, with organic carbon concentrated near the surface and decreasing regularly with depth. The organic acids that produce E horizons at higher elevations also cause extremely acid conditions (pH 4.1–5.2), whereas lower-elevation soils are less acidic (4.8–6.2). The morphological and chemical expression of podzolization in these soils increases with elevation, presumably coinciding with decreased temperature and increased effective precipitation. The soils at the higher elevations are Spodosols, whereas those at lower elevations are Inceptisols. Spodosols in the Klamath Mountains appear to be forming just over the climatic threshold required for podzolization.