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Discussion of the Quaternary geology of the Sixmile watershed is logically separated into two sections: the Sixmile-Willseyville Trough and the upper Sixmile drainage, both of which can be further divided into sub-units based on geological characteristics. The Sixmile Trough section displays evidence for 4 glacial advances based on morphologic and/or lithologic criteria. The oldest advance is associated with the broad U-shaped upper valley slope section and is possibly pre-Illinoian. The probable Illinoian age of an inner glacial trough is derived from the assumed Sangamon age of a very large interglacial gorge incised into the floor of that trough. The inner glacial trough is overlain by an array of mid- Wisconsin (Cherrytree stade) deposits that document a glacial advance that reached into the Sixmile Trough. An interstadial gorge was cut into the base of the Sangamon gorge, probably following the mid Wisconsin glaciation but before the Late Wisconsin glaciation, which overrode the entire area and overprinted most of the earlier glacial features.

The ice front retreat from the Late Wisconsin glacial maximum (Nissouri stade) is best documented in the Willseyville Trough and upper Sixmile drainage. Well data indicate that the ice front during the Erie interstade did not retreat far north of the Sixmile-Willseyville trough-upper Sixmile junction, which would explain the single Late Wisconsin till in the Sixmile Trough. The subsequent Port Bruce readvance produced the Valley Heads moraines, which are characterized by large outwash plains but few end moraines or lateral moraines on the interfluves. However, several such moraines and ice margin channels in the upper Sixmile drainage outline the shape of the Port Bruce ice front there. Ice stagnation following the Port Bruce advance led to extensive kame and kettle terrains behind the ice front maxima and to a small lake trapped between the Willseyville Trough and Upper Sixmile valley. A large delta fed sediment from the upper Sixmile basin into this lake. Till interbedded with the deltaic foresets demonstrate that active ice closed this lake at times. The lake drained, probably catastrophically, through a large channel, here termed the Willseyville channel, now marked by a series of wetlands separated by alluvial fans. A minor “Brooktondale” re-advance is marked by a till overlying the delta and by a lateral moraine that can followed from the east side of Inlet Valley across the interfluves into the Sixmile Creek valley and onto its northern slope. The Brooktondale re-advance is here correlated with the Hatfield event in New England and the Little Falls re-advance in the Mohawk valley, at about 13.25 14C ka BP. An unusual channel, located at the front of this ice advance near the Brooktondale delta, changes its downstream direction 180 ° from southerly to northerly and cuts across and downward through the delta. It is most easily explained as an englacial to subglacial channel that drained NW under the ice of the Sixmile Trough. This would require subglacial drainage down the Sixmile Trough and northward along the Cayuga Trough into the Mohawk valley, which was ice-free at this time. Sub-glacial drainage at this time would explain the lack of lacustrine sediments in the southeast section of the Sixmile Trough. Subglacial drainage was apparently soon blocked and a proglacial lake formed in the Sixmile and Cayuga troughs because a deltaic or lake marginal, coarsening upward sequence of fine sand to gravel overlies the till in the northwest section of the Sixmile Trough. A planar cap of coarse gravel and cobble descends northwesterly along the Trough from an elevation of approximately 780’ at the 30’ dam to 600’ at Van Natta’s dam, indicating a rapid decreasing surface elevation of this proglacial lake. This decrease in elevation is attributed to the retreating Laurentide ice front, which is recorded by recessional moraines north of Ithaca.

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Quaternary Geology; Sixmile Creek


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