Southwest of the Rose Canyon fault, which in Rose Canyon displaces rocks on its southwest side, an Eocene marine cobble conglomerate and sandstone unit, designated the Mount Soledad Conglomerate (part of the Rose Canyon Shale Member of Hanna, 1926), rests unconformably on Upper Cretaceous rocks of the Cabrillo Formation. This formation crops out around the Mount Soledad anticline in La Jolla and northern Pacific Beach and south of Mission Bay on the southwest flank of the Pacific Beach syncline. At its type locality on Mount Soledad, the formation is 49 m thick and consists of cobble conglomerate with minor beds of sandstone. The conglomerate content of the formation is variable to the southeast where it is locally composed entirely of medium-grained sandstone, The conglomerate commonly overlies similar Upper Cretaceous conglomerates of the Cabrillo Formation. The presence of distinctive red porphyritic, soda rhyolite-tuff clasts in the Mount Soledad Formation differentiates it from the Cabrillo Forrnation. This difference is easily seen at a sea-cliff exposure 300 m: northwest of the end of Tourmaline Street in Pacific Beach where the two conglomerates are in contact. The sandstone is moderately well sorted, subanguiar to subrounded, poorly indurated, and well bedded. It consists of quartz (75-80 percent), potassium feldspar (20-25 percent) , plagioclase (1-2 percent), biotite (1-2 percent), and a trace of epidote, pyroxene, and hematite. The Ardath Shale, conformably overlying the Mount Soledad Formation, contains fossils which are lower middle Eocene in age (Bukry and Kennedy, 1969). The Mount Soledad Formation correlates with the basal part of the Santiago Formation in the Santa Ana Mountains (Kennedy and Moore, 1971a).

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

Bukry, David, and Kennedy, M.P., 1969, Cretaceous and Eocene coccoliths at San Diego, California, in Short contributions to California geology: California Division of Mines and Geology Special Report 100, p. 33-43.
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.