J. B. Woodworth (1901) described the "Port Washington deltas" from exposures of the topsets and foresets of several Gilbert-type deltas in two of the large Port Washington sand pits. He inferred that these deltas had built into a lake with water plane at +80 ft (MSL ref.).

Storms during the 1992-93 winter have exposed another Gilbert-type delta with foresets dipping S lying ca. 0.5 mi NW of those illustrated by Woodworth. The horizontal topset/foreset boundary, which marks the former water plane, lies at an altitude of about +40 ft. An additional 10 to 15 feet of coarse, pebbly fan sediment prograded across the horizontal delta plane that previously had been built out at the former lake level. Overlying the fans is about 3 feet of till and 2 feet of loess. The foreset beds extend at least to MSL; no bottomsets are exposed.

Woodworth inferred that the Gilbert-type deltas had been built into a proglacial lake dammed on the SE by the Harbor Hill moraine ridge and are therefore younger than the Harbor Hill moraine. We do not know the age of the newly exposed delta, but based on striated bedrock- and provenance data that the Harbor Hill moraine was built by ice that flowed from NW to SE (its age may be Illinoian), we infer that the delta is pre-Woodfordian (the Woodfordian ice flowed from the NNE to the SSW).