This study describes a relatively pristine salt marsh and ecotones that could serve as a comparison for understanding disturbed West Coast marshes. The salt marsh and terrestrial transitional vegetation of Bahia de San Quintin is composed of a low number of species with only a few dominants, and it is similar to southern California marshes. Species react to minor elevational differ- ences to create vegetation patterns or gradients, with each species reaching its highest frequency in the higher drier portions in a particular part of the marsh. Salicornia virginica has the broadest amplitude of occurrence. Plant cover increases with elevation which corresponds to decreases in tidal inundation, saturated soils, and salinity. Frequencies of species were low and variable in the marsh-upland transitions, but were high and consistent in the marsh proper. The presence of capillary extensions of tidal waters appears to be a critical factor in controlling the distribution of species in the ecotone areas. The establishment of submerged Zostera marina beds blocks the open body of water and initiates successive development that may culminate in terrestrial vegetation by contributing to its stabilization and sedimentation. Piles of detached Zostera mat down the emergent vegetation which results in open pockets that are eventually revegetated.