Autonomous underwater vehicle measurements are used to quantify lateral dispersion of a continuously released Rhodamine WT dye plume within the stratified interior of shelf waters in northern Monterey Bay, California. The along-shelf evolution of the plume's cross-shelf (lateral) width provides evidence for scaledependent dispersion following the 4 /3 law, as previously observed in both surface and bottom layers. The lateral dispersion coefficient is observed to grow to 0.5 m 2 s 21 at a distance of 700 m downstream of the dye source. The role of shear and associated intermittent turbulent mixing within the stratified interior is investigated as a driving mechanism for lateral dispersion. Using measurements of time-varying temperature and horizontal velocities, both an analytical shear-flow dispersion model and a particle-tracking model generate estimates of the lateral dispersion that agree with the field-measured 4 /3 law of dispersion, without explicit appeal to any assumed turbulence structure.