The Catalina Schist (southern California), contains variably metamorphosed mafic, sedimentary, and ultramafic rocks that were accreted at depths of 15 to 45 km during early Cretaceous subduction. Fluid flow in the Catalina Schist was concentrated along fractures and shear zones, as indicated by the textures and abundance of veins and evidence in melange zones for metasomatism and homogenization of stable isotope compositions. Slab-parallel orientations of major melange zones with enhanced permeability may dicate that the majority of fluid released by devolatilization at depths >15 km in subduction zones moves updip toward the seafloor. Such transport could contribute to fluid budgets in shallower parts of accretionary wedges and facilitate large-scale mass and energy transfer in forearc regions. ¿American Geophysical Union 1991