Petrographic modal analyses of sandstone samples from the Upper Cretaceous Guinda, Forbes, Kone, Marsh Creek, Chico, Starky, Winters, and Mokelumne River formations of the Sacramento basin reveal that samples are dominated by plutoniclastic and volcaniclastic detritus, have intermediate plagioclase-to-total=feldspar ratios (0.48-0.65), and have high but variable L{sub v}/L ratios (0.51-0.80). Forbes/Kione sandstones, in comparison to Starkey/Winters samples, have higher proportions of volcaniclastic (plagioclase) to plutoniclastic (Q{sub m}, K) detritus and higher W{sub p}/total Q and L{sub m}/L{sub v} ratios. The Chico Formation, like the Starkey/Winters, is dominated by plutoniclastic material; in comparison to Forbes/Kione samples, the Chico has higher total lithic values (L{sub t}), especially in the L{sub m} fraction. These data strongly support derivation of the sands from the Cordilleran magmatic arc system to the north and east. Sandstones from the Chico, Starkey, Winters, and Mokelumne River formations were derived primarily from the dissected Sierran magmatic arc complex to the east, with a minor but significant secondary source in foothill belt metamorphic complexes. Forbes and Kione sandstones, in contrast, appear to have been derived from the Idaho Batholith and Blue Mountain regions of Idaho/Oregon to the north and northeast. When corrections are applied to account for significant diagenetic dissolutionmore » of plagioclase and compactional alteration of lithic fragments (especially L{sub v}), the dissected or transitional arc provenance for most samples is strengthened. Modal data and paleogeographic reconstructions suggest that during the early and middle Campanian, most detritus in the Sacramento basin was derived from the north/northeast (erosion of the Idaho batholith arc system), reflecting southward progradation of the Kion/Forbes delta-submarine fan system into the longitudinal forearc basin.« less