The Mission Valley Formation is composed of marine, lagoonal, and nonmarine sandstone that lies conformably upon the Stadium Conglomerate and is conformably overlain by the Pomerado Conglomerate. The Mission Valley Formation has a maximum thickness of 60 m and was named for exposures along the south wall of Mission Valley on the west side of State Highway 163 in the adjacent La Jolla quadrangle (Kennedy and Moore, 1971). The sandstone is characteristically soft and friable, light olive gray, and fine to medium grained. It is locally interstratified with carbonate cemented beds. Cobble conglomerate tongues within the Mission Valley Formation, which are identical to the Stadium Conglomerate in lithology, comprise up to 30 percent of sections measured in the easternmost exposures but less than 15 percent of sections measured in the western part of the area. Due to the friable nature of the Mission Valley Formation, it lacks the bold topographic expression of the resistant conglomerate formations that lie stratigraphically above and below. Thin deposits of conglomeratic slope wash commonly mask the Mission Valley Formation in the eastern part of the area, where it is overlain by the Pomerado Conglomerate. The slopes developed in this area are relatively steep on the Pomerado Conglomerate, shallow on the Mission Valley Formation, and steep on the Stadium Conglomerate. An understanding of these topographic relationships helps to determine the distribution of the Mission Valley Formation in areas where it is covered by surficial deposits. The Mission Valley Formation thins from west to east, pinching out in the eastern part of the Poway and La Mesa quadrangles. The rock contains an upper Eocene molluscan fauna. An assemblage collected from the uppermost beds of the Mission Valley Formation in a road cut 200 m due east of the Miramar Reservoir filtration plant (elevation 238 m) at Lat 32 degrees 54.8' N.; Long 117 degrees 05.7' W. includes Tellina tehachapii Anderson and Hanna, Macrocallista Andersoni Dickerson, Crassatella uvasana s.s. Gabb, and Turritella uvasana sargeanti (Anderson and Hanna). These species when considered together are indicative of the upper Eocene age (Tejon Stage) and correlative with the upper Eocene of Europe (Givens, 1974).
The Mission Valley Formation is part of the Poway Group. The Poway Group (Poway Conglomerate of Hanna, 1926) includes three partly intertonguing and partially time equivalent formations, the Stadium Conglomerate, the Mission Valley For- mation, and the Pomerado Conglomerate. These rocks are primarily nonmarine in their easternmost exposures and nearshore marine and lagoonal in their westernmost exposures.

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

Givens, C.R., 1974, Eocene Molluscian biostratigraphy of the Pine Mountain area, Ventura County, California: University of California, Dept. of Geol. Sci. Bull., v. 109, 107p.
Hanna, M.A., 1926, Geology of the La Jolla quadrangle, California: University of California, Dept. of Geol. Sci. Bull., v. 16, p. 187-246.
Kennedy, M.P., and Moore, G.W., 1971, Stratigraphic relations of Upper Cretaceous and Eocene Formations, San Diego coastal area, California: Amer. Assoc. Petroleum Geologists Bull., v. 55, p. 709-722.