1953 USGS Bedrock Map, Island Pond Quadrangle
This Bedrock map shows the west side of Nulhegan basin, notice the abrupt half circular shape of the bedrock around the floor of the basin, it is composed mostly of igneous rock types, the most abundant of which are Nulhegan Monzonite Quartz, and Biotite. Nulhegan Monzonite is a medium to course grained form of quartz. The rock type most commonly associated with terrestrial craters is shocked quartz, which is a type of quartz which has been deformed by the extraordinary heat and pressure caused only by extremely large impacts. There is a possibility that Nulhegan quartz may have the same characteristics as shocked quartz but further investigation is needed for confirmation.