Included in the tract studied are four sedimentary formations and the recent alluvium. These formations are in the order of their deposition: the Mint Canyon, the Modelo, the Saugus, and the old alluvium or terrace deposits. The Mint Canyon and the Saugus formations are both of terrestrial origin; the Modelo is of marine. The area is of especial interest because each of the beds rests unconformably [cq] on the next under it, and because the boundary of the basin of deposition is included in its extent. This evidences itself with the thinning of the Modelo and the overlapping of the Saugus onto the Mint Canyon. There has also been deformation and minor faulting, especially in the northern portion.