The Delmar Formation (Delmar Sand Member of Hanna, 1924) is exposed from the northern edge of the area mapped for 9 km south to Soledad Valley where it is overlain by younger rocks. Most of the Delmar Formation is dusky yellowish-green sandy claystone interbedded with medium-gray coarse-grained sandstone. Several resistant beds composed of Ostren idriaensis Gabb and other brackish-water mollusks indicate a lagoonal origin. The sandstone is typically composed of quartz (80-85 percent), potassium feldspar (10-1 5 percent), plagioclase (1-2 percent), biotite (2-3 percent), and a trace of hematite, topaz, glauconite, and pyroxene. The claystone is composed of montmorillonite and kaolinite. The base of the formation is not exposed but is presumed to rest unconformably on Upper Cretaceous or older rocks or conformably on the Mount Soledad Formation as do correlative formation to the north and south. In its type section near the town of Del Mar and throughout the area, it is overlain gradationally by the Torrey Sandstone, with which it is also partly equivalent. In the subsurface, 45 km north gear Carlsbad, the Delmar Formation grades into the Santiago Formation, and its bourndary with the Santiago Formation occurs directly below the northernmost depositional limit of the overlying Torrey Sandstone (Kennedy and Moore, 1971a). The Delmar Fornnation is considered to be middle Eocene in age because it is correlative in part with the Mount Soledad Formation on the south, the Santiago Formation to the north, and contains a rich Domengine molluscian assemblage.

Source - Geology of the eastern San Diego metropolitan area, California (Del Mar, La Jolla, Point Loma, La Mesa, Poway, and SW 1/4 Escondido quadrangles), 1975, California Div. Mines and Geol. Bull. 200, Section A, by Michael P. Kennedy

References

Hanna, M.A., 1926, Geology of the La Jolla quadrangle, California: University of California, Dept. Geol. Sci. Bull., v. 16, p. 1 87-246.
Kennedy, M.P., and Moore, G.W., 1971a, Stratigraphic relations of upper Cretaceous and Eocene formations, San Diego coastal area, California: American Assoc. Petroleum Geologists Bull., v. 55, p. 709-722.