Cretaceous marine forearc basin strata exposed in the northwestern Vizcaino Peninsula of west-central Baja California record an abrupt change in paleogeography at -99 Ma, close to the Albian-Cenomanian boundary. The Albian Los Cbapunes Formation comprises turbiditic mudstone and minor sandstone interpreted as deep marine basin-plain deposits. These rocks are overlain disconformably by early to mid-Cenomanian boulder-cobble conglomerates with interbedded sandstone turbites that records active faulting and uplift. Large clast sizes (abundant meter-sized clasts), angularity of matrix granules, fluid escape structures in sandstone, and slumping in thin-bedded intervals indicate derivation from a proximal source to the north and slumping in thin-bedded intervals indicate dervation from a proximal source to the north and rapid deposition on submarine slopes. Volcanic rocks make up -84% of the clast population with no major variability detected at 5 sites where counts were made. The volcanics are mainly intermediate to silicic composition. Potassium-feldspar rich granitoids make up most of the remainder of the clasts with subordinant sedimentary and metamorphic clasts including quartzite. Magnetic susceptibility values of 499 granitoid clasts measured with a Geoinstruments JH-8 susceptibility meter vary widely over four orders of magnitude; these values are consistent with a mixed western/eastern zone Peninsular Ranges batholith source, and a potential unknown source. A biotite granodiorite clast yielded a concordant 135-140 Ma zircon U/Pb crystallization age. The zircon age and the dominance of K-rich graoitoids, are inconsistent with a PRB source for the Cenomanian conglomerates. The Vizcaino arc and ophiolite basement is also a possible source area, but the presence of K-rich granitoids and quartzites clasts are also inconsistent with the local basement lithologies.