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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 scale, including peak subsidence of 160 +/- 4.4 mm/yr occurring just inland of the levee of the westernmost island and average subsidence of 11 mm/yr along the planned path of water conveyance tunnels through the Delta. The results are compared to local sea level rise (SLR), measured at a tidal gauge in San Francisco Bay, to show that subsidence is currently the dominant contributor to local relative sea level rise (RSLR) by nearly a factor of five. Based on recently measured and modeled acceleration of SLR, subsidence in the Delta is likely to dominate RSLR until the middle of the 21th century.