The Kendall-Frost marsh reserve located on the Northern edge of Mission Bay in San Diego, CA once spanned over 2,000 acres along the coast of the bay. The area underwent heavy dredging and construction starting in the 1940s that removed nearly all the natural marshes. Today, only a small 40-acre plot remains. Rising global temperatures are causing thermal expansion of the oceans and melting of land based ice. This unprecedented warming is causing sea levels to rise at an increasing rate. The current rate of global sea level rise is 3.4mm/year. The overall projected sea level rise by 2100 is estimate to be between 0.5-2m. This increased rate threatens to outpace sediment accretion of coastal wetlands which will cause major alterations to the salt marshes, including the Kendall-Frost marsh reserve. Sea Level Affecting Marshes Model (SLAMM) is a useful tool for simulating the effects of rising sea levels on salt marshes, but its use relies heavily on accurate accretion data. This study was aimed at determining accurate rates of accretion for the Kendall-Frost marsh reserve using a relatively simple and inexpensive method. Sample cores of the marsh were taken using a hand-corer 1m in length. Cores were sectioned into 1cm lengths and were analyzed for stable lead (Pb207) content using an ICP-MS. A peak was identified which correlated to the ban of tetraethyl lead (TEL) in gasoline which corresponded to 1973. From this peak in lead levels, sediment chronologies were then developed and used to determine accretion rates for the marsh. Peaks were identified at depths which correlated to an average accretion rate of 4.17mm/year since 1973. This accretion rate is slightly lower than the accretion rate used by most studies of the area. This lower accretion rate, when used for SLAMM modeling of wetland alteration for Mission Bay, indicates that loss of the Kendall-Frost saltmarsh under future sea level rise scenarios will be greater than previously modeled.