Geology of the Los Angeles Basin, California: an introduction

The physiographic basin is underlain by a deep structural depression; the buried basement surface has relief of as much as 4.5 miles in a distance of 8 miles. Parts of this depression have been the sites of discontinuous deposition since late Cretaceous time and of continuous subsidence and deposition since middle Miocene time. In middle Miocene time this depositional basin extended well beyond the margins of the present- day physiographic basin. The term ''Los Angeles basin'' refers herein to the larger area. The evolution of the basin is interpreted in 5 major phases, each of which is represented by a distinctive rock assemblage--the predepositional phase and basement rocks, the prebasin phase of deposition and upper Cretaceous to lower Miocene rocks, the basin-inception phase and middle Miocene rocks, the principal phase of subsidence and deposition and upper Miocene to lower Pleistocene rocks, and the basin disruption phase and upper Pleistocene to Recent deposits. The Los Angeles basin in California's most prolific oil- producing district in proportion to its size: at the end of 1961, its cumulative production (5,035 billion bbl) was nearly half that of California's. (103 refs.)