The Ilgachuz Range is the second largest shield volcano in the Anahim Volcanic Belt which includes other immediately nearby ranges, the Rainbow Range and Itcha Range. It stands at above sea level - slightly shorter than its neighbor, Rainbow Range. It has a diameter of . The Ilgachuz Range was created by two chemically separate magmatic periods; an early complex series of trachyte and rhyolite eruptions, and late extrusion of a sequence of basaltic lava flows. Evacuation of the volcano's magma chamber resulted in the failure of one or more centrally located calderas. It is divided into Precaldera, Dome Forming, Intra Caldera and Shield Forming assemblages.