Chestnut [Castanea dentata (Marsh.) Borkh.] was a dominant tree of the upland forests of eastern North America until its elimination by the blight fungus, Endothia parasitica Anders. The blight originated in New York City in 1904, and within 50 years, it spread throughout the entire range of Castanea dentata. The chestnut destruction is documented in lake sediments by a corresponding decline of chestnut pollen as illustrated in examples from Lakes Ontario and Erie, and Woodcliff Lake, New Jersey. According to the data from Woodcliff Lake, the decline can be assigned an age equivalent to the time of the chestnut die-out for the area. Thus, dates of 1930 A.D. and 1935 A.D. are taken to represent times of the chestnut pollen decline in Lakes Ontario and Erie, respectively. The Castanea pollen decline provides an excellent and very recent time horizon (above the Ambrosia pollen boundary) for determining sedimentation trends since the time of European settlement as well as recent sedimentation rates.