Abstract: Unconsolidated strata of clay, silt, sand, and gravel of Late Cretaceous and pre-Wisconsin Pleistoscene ages lie between crystalline basement rocks (bedrock) of Precambrian (?) age and unconsolidated deposits of late Pleistocene (Wisconsin) and Holocene ages in Queens County, Long Island, N.Y., a borough of New York City. Data collected during a recent study of the hydrogeology of the county and updated records of earlier studies have been used to prepare contour maps that delineate the surfaces of the bedrock and the Upper Cretaceous and pre-Wisconsin Pleistocene deposits. The presence of diabase fragments, apparently from the Hudson Palisades, in a buried valley through the county suggests that the ancestral Hudson River was diverted into Queens County in Pleistocene.