The major edifice, which consists of light gray, basaltic andesite lava flow deposits, sits to the west of the first tephra cone. Variegated pyroclastic rock is embedded among these flows. Element abundance analysis suggests that lava in the Three Fingered Jack area can be grouped into discrete units based on its source magma chamber, except for the Jorn Lake basalt produced by the underlying shield volcano and basaltic andesite erupted by Three Fingered Jack. Petrological analysis shows high and low pressures for the crystallization of these lava flow deposits, and that basaltic andesite was distinct from basalt due to longer fractionation times.