Sandy siltstone and fine-grained sandstones are interbedded with the aforementioned rock types. The Monterey Formation is characterized by abnormally high silica content compared to most clastic rocks. There are also silica-cemented rocks known as porcelanite and porcelanite shale. While this formation has distinguishable beds, there are many shale, sandstone, and mudstone beds that have normal amounts of silica. This sequence of this formation indicates an off-shore marine environment. The Fernando Formation is split into two sub-facies known as the Pico and Repetto Members. These members represent a distinct change in the depositional environment and are of Pleistocene age. The Repetto is the older of the two members and is composed of interbedded fine to coarse grained siltstone, mudstone, and sandstone. The Pico Member is mostly made of massive siltstones and sandstones interbedded with minor silty-sandstones. Holocene alluvium and Quaternary sediments is a largely unconsolidated unit and is composed mostly of gravel and floodplain sediments. The sediments that mark the top of the basin can be found in modern streams/rivers and at the base of the foothills. Tectonic setting The history of this basin begins with the subduction of Pacific plate underneath the North American plate in the beginning of the Mesozoic. During this subduction event, two smaller plates, the Monterey and Juan de Fuca plates, also began to subduct underneath the North American plate. Around 20Ma, the Monterey plate attached to and followed the motion of the Pacific plate. Later, subduction of the Pacific-Monterey ceased and the plate margin was converted to a transform boundary. The North America/Pacific-Monterey transform boundary began to move north and created crustal extension. This rifting was accompanied with the rotation of the western Transverse Ranges. This rotation is responsible for the placement and northwest-southeast orientation of the LA Basin. Early in the Miocene, before deposition of the Topanga, high heat flow and transtension caused the extension of the basin. As the crust thinned, the basin began to subside from isostatic pressure as a result of large amounts of sediment deposition. Because the basin lies on the boundary of the Transverse and Peninsular Ranges, this basin experiences both compressional and strike slip tectonics. During the early Pliocene, also identified as the "Basin Disruption" phase, deformation and folding occurred as a result of fault movement and a slight rotation event. While movement along the San Andreas Fault is responsible for the placement of the basin, it is