The Newport-Inglewood zone is a 45 mi long narrow belt of en echelon folds and faults which trends southeast through Miocene-Pleistocene sediments of the Los Angeles basin. Below is an inferred right slip fault, presumed to follow a contact separating the oceanic Catalina Schist facies from an eastern continental basement facies of granitic and associated metamorphic rocks. The Newport-Inglewood zone of deformation disappears abruptly on the northwest at the faulted south front of the Santa Monica Mountains, and it apparently ends gradually to the southeast near Newport, California. Displacement on the inferred basement fault, which is responsible for deformation in the overlying strata, mainly reflects Pliocene-Holocene north-south shortening (Pasadenan orogeny). The contact between oceanic and continental basement rocks is inferred to continue offshore, southeast of Newport, under Cenozoic and probably Late Cretaceous strata. These strata apparently are not deformed in a belt of folds and faults, as in the Los Angeles basin.
The basement rock contact is inferred to continue to the southeast, passing along the west side of Baja California, for a total distance of more than 800 mi. It is assumed to have developed by a sea-floor contraction mechanism of east-west shortening in Cretaceous time (perhaps a late and western element of the Nevadan orogeny). It is named here the Southern California subduction zone, and it should not be confused with the Newport-Inglewood zone of deformation which developed over its northern segment at a later time and within a different strain system. This basement zone, along with what are called here the Coast Ranges and Great Valley subduction zones, are considered to mark the position of a Mesozoic oceanic trench which originally extended for more than 2,000 mi along the margin of the northeast Pacific Basin.