By the end of the 19th century extensive portions of the shoreland had been converted to large estates, many of them still standing today. The Hudson is tidal freshwater at the Tivoli Bays, with an average tidal range of 3.9 feet. The Stony Creek drains into Tivoli North Bay and the Saw Kill drains into Tivoli South Bay. Tivoli North Bay's predominantly intertidal marsh has a well-developed network of tidal creeks and pools. A similar network of creeks and pools is beginning to form in Tivoli South Bay's shallows and mudflats.
Bedrock is Ordovician gray sandstone and shale.
Upland soils in the area are primarily derived from glacial till and Lake Albany clays. Soils at the site include muck, made land, and a variety of loams, including silty clay, silt, fine sandy, and gravelly loams. The bottom of the bays is largely soft muck, as much as 25 feet deep. The tidal swamp between North and South Bay has eight feet of peat overlying silt. L. MAPS Contact the Reserve for more information.