During at least three glacial periods, including the Wisconsin glaciation around 20,000 years ago, ice sheets advanced south across North America carving moraines, valleys, and hills. In particular, bays and estuaries were formed along the north shore of Long Island. During glaciation, the meadows surrounding the Flushing River were formed just north of the terminal moraine that runs across Long Island, which consisted of sand, gravel, clay and boulders. The moraine created a drainage divide, with rivers north of the moraine such as the future Flushing River emptying into the north shore. The Flushing Meadows site became a glacial lake, and then a salt marsh after the ice melted. Prior to glaciation, the Flushing River valley was used by the Hudson River to drain southward into the Atlantic Ocean. Through the 19th century, wetlands continued to straddle Flushing River. Species inhabiting the site included waterfowl and fiddler crab, with fish using water pools for spawning.
