Geology
Like other volcanoes in southwestern British Columbia, Mount Cayley lies within the Coast Plutonic Complex, which is the single largest contiguous granite outcropping in North America. The intrusive and metamorphic rocks of the Coast Plutonic Complex extend approximately 1,800 kilometres (1,100 mi) along the coast of British Columbia, the Alaska Panhandle and southwestern Yukon. This is a remnant of a once vast volcanic arc called the Coast Range Arc that formed as a result of subduction of the Farallon and Kula Plates during the Jurassic-to-Eocene periods. In contrast, Mount Cayley, Mount Meager, Mount Garibaldi and Silverthrone Caldera are of recent volcanic origin.
Mount Cayley consists mostly of an igneous rock with a high iron content called dacite, although another igneous rock, rhyodacite, with intermediate composition of dacite and rhyolite is also present. Unlike many of the other volcanoes further south, Cayley does not dominate the surrounding landscape, which consists of high, rugged peaks.
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