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The Sacramento-San Joaquin Delta, like other heavily engineered deltas throughout the world, has undergone substantial subsidence since the late 1800s when the natural estuary was leveed to form islands. Today, islands within the Delta have subsided to the point where most lie below mean sea level. Long-term sustainability of the Delta requires reversal of subsidence, but spatially comprehensive maps of subsidence have not been available to inform and monitor remediation. Reported here is the first spatially dense map of recent subsidence rates across the Delta, based on synthetic aperture radar interferometry and constrained by GNSS observations. The analysis uses a temporally dense and spatially overlapping set of data acquired by the Uninhabited Aerial Vehicle SAR (UAVSAR) sensor in 2009–2015. On average, the Delta is subsiding by 9.2 ± 4.4 mm/yr with high variability even at the sub-island …