Two years ago, W. P. Woodring and M. N. Bramlette of theUnited States Geological Survey completed a geologic map of the Palos Verdes Hills. A report on the area by Mr. Woodring is now in course of preparation. Shortly after completion of the field work, excavation began on the Whites Point Outfall Sewer Tunnel, which penetrates the entire eastern portion of the hills. Since natural exposures are rare in this part of the area, Mr. Woodringtook the opportunity to supplement the surface data by subsurface information afforded by the tunnel. The writer was given a temporary appointment with the Survey, and with the aid of knowledge brought together by the above workers, made a detailed study of the geology of the tunnel.
In a work of this kind much of the interest centers uponthe question as to how far a structure section constructed from surface data may be relied upon at depth. Examination of figures 1 and 4 discloses that the surface work was accurate to au almost surprising degree.
The Whites Point Tunnel was constructed by Los Angeles Sanitary District No. 2 for the purpose of sewage disposal, which was formerly taken care of by a plant in Harbor City. The route shown in figure 1 was chosen by the District on recommendation of Dr. Buwalda and others, who considered the "hard" rocks of the Palos Verdes Hills a better foundation in event of earthquakes than the almost unconsolidated sands underlying the extension of the Los Angeles city boundary into Wilmington.
The tunnel extends from the intersection of Vermont Avenue and Lomita Boulevard in Harbor City to Whites Point, a distance of nearly six miles. An open out for the conduit joins the north portal with the intake. On the southern end a concrete pipe terminates 5,000 feet from shore, and at a depth of approximately 150 feet. Throughout the entire length the floor of the tunnel is 12 feet below sea level. The bore is a horseshoe in section and approximately 10 feet in diameter, but this was later increased to 11 feet in certain parts of the section between stations 102 and 180. The total estimated cost is in the neighborhoodof $2,500,000, the funds being tarnished by Los AngelesSanitary District No. 2, and the Public Works Administration(P. W. A. Project 7133). Excavation began in September, 1935and was completed on October 14, 1936. During this time thewriter kept in close contact with progress of tunneling operations. Except where imperfect consolidation of the rock necessitated very close timbering, the data were obtained from an almost continuous exposure. Since the general trend of the tunnel is approximately normal to the regional strike, this information can be used for constructing a structure section through the eastern portion of the Palos Verdes Hills.
