Structure of the Northwestern Puente Hills, Los Angeles County, California

Abstract

The structure of a part of the northwestern Puente Hills, about four miles east of Whittier, California, is characterized by north dipping marine sandstone, conglomerate, and shale of Upper Miocene and Lower Pliocene ages. These sediments form the north limb of a broad regional anticline that has been faulted by the high-angle Whittier thrust fault which is located just south of the mapped area. The compressive forces that formed the Whittier fault are responsible for additional minor faulting and folding of the area covered in this report. There are two main fault systems in the area, the Rowland fault system and the English fault system. The Rowland fault system consists of a main high-angle thrust fault with two spur faults. This system has produced some minor folding, some of which Shoes overturning, and some just reversal in dips. Many of the folds have been due wholly to the drag effects of the faults, others due to compressional forces, while still others represent a combination of the two forces. The English fault system marks a change in the general strike of the formations. To the east of this system the formations trend east-northeast, and to the west of the system the trend is west-northwest. The only flexure that is not apparently connected with faulting is a broad plunging nose or anticline called the Repetto nose. Small anticlinal folds in the southern part of the area may reflect buckling north of theWhittier fault.