Most studies of sediment budgets along coastlines divide the coast into "littoral cells". The Oceanside Littoral Cell, which begins at Dana Point and extends south to the heads of Scripps Submarine Canyon derives most of it's sediment from the rivers within the system such as the Santa Margarita River which is the subject of this report.To determine the amount of sediment the Santa Margarita River deposits during Spring of a given yearItook water samples at high and low tide, before and after a rainfall and recorded the river flow velocity. By using a mill·ipore filter system I found that there was more beach sediment in the water at all times except after aO.OJ inch rainfall. The increased amount of water flowing out to sea contained more silt sized or river erived sediment than beach sand which indicates active deposition. The river flow velocities did not fluctuate much between high and low tide although at very high tides there was no flow out of the river mouth. The Santa Margarita River is therefore a major sediment cource for the Oceanside Littoral Cell but only after significant rain fall. The contribution of sand to the beaches has become more significant as new dams have intercepted the flow of sediment from other rivers in the Oceanside Littoral Cell.