Chemical quality and discharge data were collected and analyzed from five streams draining watersheds between Half Moon Bay and Santa Cruz, California, to determine the contribution of atmospheric chloride to these coastal basins. Fifty‐nine percent of the total chloride leaving the basins underlain by Tertiary sedimentary rocks per year is atmospheric in origin. Nineteen percent of this atmospheric chloride contribution is introduced dissolved in rainwater, whereas the remaining 40% is brought into the basins as fine particulate dust, in ‘fog drip,’ or as an aerosol.