Geology
Buttermilk Falls divides Oatka Creek into two distinct geological regions. The upper stream's bedrock is local sedimentary rock formations, with the shales and sandstones of the Sonyea Group, shale-limestone Genesee Group and Tully Limestone dominating from the headwaters to Pavilion. Between there and Le Roy the shales and thin limestones of the Hamilton Group underlie the creek.
North of Le Roy, the Oatka becomes a losing stream, with water disappearing into the ground. In the warmer months this results in the creekbed drying up above Buttermilk Falls, and slowly re-emerging further down from springs and seeps. After it does, and turns to the east, it flows over the Akron Dolomite, Bertie Group of dolomitic shales, and the Salina Group. The latter is diverse, including evaporites such as halite and gypsum in addition to its limestones and shales.
In the lower section of the creek there is significant groundwater entering the creek. As it discharges, it weathers the gypsum and limestone. This results in increased sulfates in the water, and bicarbonates and calcium have also been found near the falls. These concentrations are in winter and spring, when heavier precipitation and runoff offsets the impact of the groundwater.
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