When the ice to the south of Munsungan wasted, it allowed the lake to drain to its present level. Consequently, Chase was then allowed to drain into Munsungan by cutting a terraced channel into the glacial deposits of the Thoroughfare. Paleoindian lithic artifacts of Munsungan chert are found only on the high terrace in the Thoroughfare while the younger archaic-age artifacts are commonly present on the lower terraces. Because of this history it is hypothesized that the lower terraces did not exist at Paleoindian time because down-cutting drainage was prevented by the ice masses primarily in Munsungan Lake and to the south of Munsungan. Hence, it is concluded that the Paleoindian presence coincided with large dissipating ice masses, and that the people occupied in the Thoroughfare area in order to procure very desirable Munsungan chert from adjacent Norway Bluff for making artifacts in the time range of 11 to 10,000 years ago.
Some hills are complex, with secondary southern axes parallel to an earlier southerly glacial flow.
GPR profiles show prograding clinoforms in the mixed-till zone, where Late Wisconsinan till overlies older till, to approximately 10 meters depth. At Marsh Hill, a distinct notch at 24 m elevation is overlain by gently inclined parallel strata, interpreted as a marine terrace. This model isolates several elongate valleys, interpreted as meltwater channels. In addition, one elongate valley would have connected to the sea in a fjard. Further topographic and geophysical study will seek similar shoreline deposits at this level.