A sedimentological investigation of recent beach sand near Cape San Blas, Florida, has revealed the presence of a number of relatively stable longshore drift cells. conceptually, the coastal cell is a closed system of erosion, transport, and deposition, bounded by points at which the longshore component of wave power is zero. Between these points, a positive littoral power gradient (erosion) complements a negative power gradient (deposition). The model has made possible computer predictions of cell and "subcell" locations for the same area, the latter term implying some leakage between neighboring systems. By using near-shore bathymetry and average wave parameters to calculate power variations, this method (if accurate) is invaluable forlocal coastal erosion studies. The sense of drift within each subcell in the study area is in the direction of decreasing grain size, increasing sorting, and a decreasing percentage of unstable minerals. Curves of mean grain size, standard deviation (a measure of sorting), and heavy mineral concentrations versus distance, correlate well with each other, and with predicted subcell locations. Counts of selected features from scanning electron microscope photographs of quartz grain surfaces also correlate, showing increasing chemical solution effects downdrift. The best correlation of data has been for the mid-swash zone for an initial wave approach direction from 1800. Three well-developed subcells here suggest that this particular level is most sensitive and hence most representative of average, longer term wave conditions. Lower beach levels appear to be more or less in constant flux, and higher levels seem to be affected by particularly high tides or storms.