Soil Development and Geomorphic Surfaces, Willamette Valley, Oregon
1970
Parsons, R. B. | Balster, C. A. | Ness, A. O.
Soil development in the Willamette Valley is related to a sequence of seven extensive geomorphic surfaces ranging in age from postsettlement to middle Pleistocene. The surfaces were mapped on high-altitude aerial photographs for an area about 7,800 km². The oldest surface associated with the present drainage system is at least 5,250-years-old and may be as old as 34,410 years. One soil series considered representative of each geomorphic surface was chosen to illustrate soil development on successively older surfaces. Soils on the most recent surfaces have developed only A1 horizons containing about 4% organic matter. Soils develop cambic B horizons within 550 years, whereas Bt horizons are formed within a period of 5,250 years. Base saturation progressively decreases from 100% in the Haploxerolls on the younger surfaces to less than 35% in the Haplohumults on the oldest surfaces.
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