Submarine canyon and onshore drainage patterns suggest that the most likely source of Pleistocene sand-sized sediment at Site 974 was the Tiber River drainage basin in central Italy, where a Pleistocene volcanic field is superimposed on Apennine orogenic rocks. In contrast, the Miocene synrift sand in Unit III may have been derived from local basement highs. The quartzolithic composition and preponderance of metamorphic and sedimentary lithic debris in sand samples from Unit II at Site 976, Unit I at Sites 977 and 978, and Unit I at Site 979 is consistent with derivation from metamorphic rocks and sedimentary cover sequences that crop out in the Betic Cordillera of southern Spain (976-978) and the Rif of Northern Africa (979); the sedimentary to metamorphic lithic fragment ratios in these samples reflect the relative proportion of metamorphic and sedimentary rocks exposed in onshore source terranes. In contrast, the source of the few quartzose Pleistocene sands at Site 976 was likely the Flysch Trough Units that crop out near Gibraltar. The significant volcanic component in certain intervals at Sites 976 (late Miocene) and 977 (early Pliocene to Miocene) is consistent with widespread volcanic activity during basin development. In general, mean sand detrital modes for sand subgroups from both the Alboran and Tyrrhenian Basin sites plot in the Recycled Orogen and Magmatic Arc compositional fields of Dickinson et al. (1983), reflecting the hybrid tectonic histories of these basins.