The Upper Cretaceous Chatsworth Formation is a sand-rich deep-sea fan deposit consisting of thick channelized sequences and interchannel deposits typical of middle fan facies. It has poorly developed outer fan lobes and slope facies. Petrographic and X-ray diffraction (XRD) data indicate the arkosic deposits of the Chatsworth Formation were derived from an uplifted granitic terrane. Paleocurrent studies indicate northward sediment transport and an east-trending slope. Regional comparisons of the Simi Hills with the Santa Ana Mountains suggest these terranes were once contiguous and covered part of a deep-sea fan system that comprised much of the Southern California area. These terranes have been offset along the Malibu-Cucamonga and Elsinore faults, and rotated in response to the opening of the Los Angeles Basin and to other adjustments in the tectonic framework of the area. The Chatsworth Formation is thought to be part of a forearc-basin deposit similar to the Great Valley sequence and not part of the Salinian borderland block. The original geographic position of the forearc basin was to the south of the Sierra Nevada Mountains and the Great Valley Sequence.--Modified journal abstract.