SOIL-LAND FORM RELATIONSHIPS OF PORTIONS OF THE SAN JOAQUIN RIVER AND KINGS RIVER ALLUVIAL DEPOSITIONAL SYSTEMS IN THE GREAT VALLEY OF CALIFORNIA.

摘要

The western slope of the Sierra Nevada has been the source of erosional detritus carried into a geosynclinal trough, presently known as the Great Valley of California, since Cretaceous times. The nature of the detritus has been a function of the climatic, volcanic, tectonic and glacial history of the Sierra which is passively reflected in the sequence of these materials deposited by both major and minor streams from the Sierra.;Properties related to diagnostic horizons which place the 52 soil series of the study area in the new taxonomy are used and evaluated for determining relative ages of selected, extensive soil series and variants. Three indexes are developed to reflect the relative ages of the selected soils. Percent-centimeter values, average percent, and grams per unit volume of pedogenic clay are calculated from full-profile mechanical analyses, bulk densities, and physical dimensions of argillic horizons within the selected soils. These indexes correlated well with the relative ages of specifically associated, nested fan surfaces of both rivers. These, in turn, relate to the Modesto, Riverbank, and Turlock Lake formations of Quaternary times. Existing patterns of mapping units of the indexed series, variants and associated soils provide additional evidence of sequentially deposited facies of the formations in remarkable detail.;Five benchmark soils and formations within or near the area have been dated by others through fossil evidence or radiometric measurement and provide ties to real time. These range from about 10,000,000 to 12,000 years B.P.;Other soils related to alluvially deposited material of Pliocene age or older are younger than their parent materials, having formed on erosional surfaces cut into these materials. Differences among these soils are related to lithologic differences in the parent materials rather than age differences. Some are probably extremely old and, even though there may be significant differences in real age, this cannot be detected by commonly used morphological measurements because of the degree of maturity in profile development. Such detection awaits more sensitive methods.;Through standard soil surveys, most of the landscapes on the east side of the San Joaquin Valley have been studied in considerable detail. The published accounts, however, cannot adequately report all geographic and pedologic data obtained. Using existing information gathered during the Eastern Fresno Area soil survey, and from adjoining areas, the systems of nested alluvial fans of both the San Joaquin and Kings Rivers have been further investigated to bring out known soil-land form relationships in greater detail, and to point out hitherto unrecorded relationships. These studies of soils and geomorphic surfaces reach back to the Eocene epoch. Most of the available information relates to the late Tertiary and Quaternary periods.;Analysis of two extremely old land forms and their soils, near the canyon mouth of the Kings River, suggests these to be correlative with the surfaces of the China Hat gravels (Upper Pliocene?) of the Laguna formation, and the somewhat younger North Merced gravels in Merced County, California. Erosional remnants of gravelly material and their soils, near the canyon mouth of the San Joaquin River, also suggest a similar relationship, but less clearly. In the northern part of the study area, relating certain marker soils to eroded upland terrain in comparison to dated Pliocene volcanic flows and associated fill of ancestral channels of the San Joaquin River provides a limited indication of the nature and development of local mid and early Tertiary landscapes.;Geomorphology and Pedology, though separate disciplines in peoples' minds, have gained much insight from each other. In the final analysis, as natural features, the landscape and the soil are inseparable.