Five cores were taken from subtidal, intertidal, and supratidal environments within the Tijuana River estuary. The Pb-210 age-dating technique was applied to the sediments of these cores. Sedimentation rates were obtained for the sediments of two cores, and these rates agree reasonably well with rates of sea level rise, storm and sewage chronology, a carbon-14 age date, and sedimentation rates obtained in other estuaries and lagoons. Pb-210 activities indicate that the rate of sedimentation has remained relatively constant for the last one hundred or so years, even though the amount of sand-sized sediment reaching the estuary has diminished as a result of the construction of dams upstream. The loss of coarse material has been counter-balanced by increased accumulation of finer sediments resulting from sewage injection in the area. Based on information from old maps and aerial photographs, the positions of tidal channels relative to core sites have changed since 1858. Slumps, bioturbation, and unconformities are common in this environment and make interpretation of the depositional history very difficult.