Quaternary tectonic influences on coastal morphology, south-central California

Abstract

The coastal morphology of south-central California is controlled largely by the rates and spatial distribution of uplifting and subsiding crustal blocks, which are bordered by Late Quaternary reverse faults that clearly disrupt marine terraces. We describe the style, rates, and locations of Late Quaternary deformation within the San Luis Range and the bordering Los Osos and Santa Maria valleys, and the influence of this deformation on evolution of the coast. The WNW-ESE trending San Luis Range, which is rising at a rate of 0.1 to 0.2 m/kyr, is bordered locally by a rugged coastline with narrow beaches and emergent marine terraces. The development and degree of preservation of the marine wave-cut platforms reflect the erosional resistance of bedrock lithologies. The marine terraces extend well inland south of Pismo Beach showing that a marine embayment existed during the Late Quaternary throughout large areas of the Santa Maria Valley. Coastal margins of the Los Osos and Santa Maria valleys, which are static or slowly subsiding, are characterized by the absence of marine terraces, and the presence of broad beaches, sand spits, and Late Quaternary dune fields. The coastal margins of these valleys are advancing seaward at average rates in excess of 5 m/kyr during the past 120 ka.