Oregon City Formation
Oregon City Formation
early Late and late Middle Jurassic, Callovian to Oxfordian
Andesite and basalt, pyroclastic breccia and tuff with lesser flow rock, very locally pillowed, and volcaniclastic sedimentary rocks.  This unit is  Included by most workers in the Smartville Volcanic complex but is separated from the main body of Smartville by a high-angle fault (Long Ravine-Spenceville fault); Creely (1965) notes a significant difference in metamorphic grade between these units. Creely (1965) reports one fossil of probable Oxfordian age from the northern part of this unit, and Saleeby and others (1989b) report a zircon U-Pb age of ~164 Ma from roughly the same area. Previously mapped as along-strike continuation of Copper Hill Volcanics to the south but note the age difference. The formally accepted age of this unit is Late Jurassic, but the ~164 Ma zircon U-Pb age indicates that it extends back into Middle Jurassic.