The Tijuana Estuary in San Diego is one of the largest and most valued wetland ecosystems remaining in southern California. Sediment is a key management problem at the Tijuana Estuary. The estuary receives sediment from four major sources: the Tijuana River and three side canyons (Yogurt Canyon, Goat Canyon, and Smuggler's Gultch); with sediment from Goat Canyon Watershed being the main concern. This study examines Goat Canyon's role of sediment accumulation in the Tijuana Estuary versus the larger Tijuana River Watershed's role on sediment accumulation in the estuary. Through field measurements, we concluded that urbanization in Goat Canyon has likely increased sediment entering the estuary and can lead to an average of 70,000 tons of sediment entering the estuary annually. In comparison, dam construction in the Tijuana River Watershed has likely decreased sediment entering the estuary. Based on the size of the watershed area, fifteen times more sediment enters the Tijuana Estuary from Goat Canyon than Tijuana River Watershed. Particle size characterization and ___Pb isotopic dating were run on three cores extracted from these two major depositional zones in the Tijuana Estuary. Two cores from the Tijuana River depositional environment exhibited an estimated average annual sediment rate of ~0.55 cm/yr. ___Pb activity in the core from Goat Canyon's depositional environment showed a much different sedimentation pattern exhibiting a substantial change in texture and source. The core shows signs of older originally deposited sediment - possibly from deeper gullies and rilling in Goat Canyon - being eroded and deposited on top of originally younger sediment - possibly from surface sheetwash in Goat Canyon. Sampling of ___Pb in Goat Canyon's surface and subsurface would help determine the source of sediment entering the estuary. Deeper cores from Goat Canyon's depositional environment are needed in order to get an average sediment rate. Knowing the source of sediment production in Goat Canyon, along with continuing core extractions, will aid in future mitigation strategies to deal with the effects of increased deposition on the estuarine ecosystem.