The type section of the Stadium Conglomerate lies near the boundary between the La Jolla and La Mesa quadrangles along the northern wall of Mission Valley near San Diego Stadium (Kennedy and Moore, 1971a). At the type section the for- mation consists of a massive cobble conglomerate with a dark yellowish-brown coarse-grained sand- stone matrix. The conglomerate contains dispersed lenses of fossiliferous crossbedded sandstone. The fossils include calcareous nannoplankton of late? Eocene age. The Stadium Conglomerate is moderately well sorted with an average clast size in the cobble range. Clasts having diameters as large as .05 m do occur but are rare. The sandstone matrix constitutes less than 20 percent of the unit, but in local stratigraphic sections individual sandstone beds and lenses con- stitute 50 percent of the unit. The highly distinctive "Poway" clasts that occur only within Cenozoic deposits of southern California and that typify the Stadium Conglomerate consist predominantly (up to 85 percent) of slightly metamorphosed rhyolitic to dacitic volcanic and volcaniclastic rocks and up to 20 percent quartzite. The source area for these clasts is controversial, and potential sources from the Mojave Desert to Sonora, Mexico, have been proposed (DeLisle et al., 1965; Merriam, 1968; Woodford et al., 1968; Minch, 1972). Based on direction of pinching and cobble imbrication, the clasts within the Stadium Conglomerate were deposited within the San Diego embayment by a westward-flowing river system. Based on clast size the conglomerates were probably derived from a now eroded source within 150 km of their present position (Kennedy, 1973a). The Stadium Conglomerate is conformably underlain by the Friars Formation and is conformably overlain by the Mission Valley Formation.
The Stadium Conglomerate 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

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