Thesis

Stream terraces as indicators of landscape equilibrium : western Tranverse Ranges, California

A landscape within the tectonically active western Transverse Ranges, California, is evaluated to determine the applicability of the dynamic equilibrium concept of landform development. It is concluded that individual landforms and gradational processes in the Lion Canyon Quadrangle area conform to postulates presented by G. K. Gilbert and J. T. Hack for equilibrium landscapes. Alluvial terraces and present day floodplains in the study area typify equilibrium forms; their hydraulic geometries represent an adjustment of form to process. Investigations of alluvial terraces indicate that debris-flows are partly responsible for transportation of material from Pine Mountain to the valleys below. Altimetric measurements allow differentiation of six distinct terrace levels covering an area of 2.3 sq mi (6 sq km), and ranging in height from 10 ft (3 m) to over 300 ft (90 m) above present day stream channels. Maximum particle sizes are greater and gradients are steeper on the terraces than in the present day stream channels. Logarithmic plots of drainage basin area against terrace height, area, and gradient yield straight-line, power function relationships suggestive of allometric changes in the Lion Canyon landscape. Evolution of the drainage network and bedrock landforms is less dependent on the time element than on the heterogeneity and spatial distribution of lithologies. Analysis of trend surface data indicates local relief is directly related to lithology. Where non-resistant formations are capped by alluvial terraces, there is a 70 ft (20m) increase in local relief attributed to the protection afforded by the terraces.

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