By analysis of a unique and extensive photographic and written record spanning several decades, we characterized the spatial and temporal scales of morphological adjustment of the inlet of the Russian River Estuary, on the California coast. We paired this record with in situ measurements of beach features to create a dataset consisting of daily values of inlet width, length, shape, and position for the period of 1991–2006. Available wave, tide, and river flow data were compared with these measurements. We show that the spatial and temporal scales associated with adjustments in inlet geometry and position are dictated by different mechanisms during periods of high and low river flow and also vary with periods of large-scale climate oscillations. Our analysis of inlet shape reveals that several classes of inlet curvature correspond to unique flow, geometry, and risk of closure conditions.