Hourly measurements of suspended sediment in situ floc size distributions, constituent grain size distributions, total concentrations, and average particle densities are presented for five depths from an 11-hour anchor station in San Francisco Bay. The flocs formed well-sorted distributions with modal sizes between 100 and 500 μm, whereas the disaggregated sediment was poorly sorted with about the same volume of material in all size classes and relatively little material coarser than 100 μm. For both types of size spectra, concentrations at the coarse end of the size distribution fall off rapidly at a size range which varied with bottom shear stress. The settling rates corresponding to the modal floc diameters were generally related to the maximum disaggregated diameters by a square relationship, but turbulence appeared to limit floc size in the coarsest samples. Both the flock and disaggregated grain size vary with total concentration, suggesting that flocs are relatively stable entities which do not change during alternating settling and resuspension.