About southeast of Lillooet Lake is the Crevasse Crag Volcanic Complex. It is about 16 million years old, situated on the summit of a glaciated mountain ridge made of Late Cretaceous and younger intrusive rocks. These form part of the large Coast Plutonic Complex, which extends along the British Columbia Coast. The Crevasse Crag Volcanic Complex comprises volcanic breccias, tuffs and plagioclase-phyric flows. Analyses of major, trace and rare-earth elements indicate that dacite, andesite and basaltic andesite lava flows form its lower flanks.