When the first geological reconnaissance of the surrounding region was published in 1925, its author, Edwin T. Hodge, suggested that the Broken Top, the Three Sisters, and several other mountains in the area constituted the remains of an enormous collapsed volcano that had been active during the Miocene or early Pliocene epochs. Naming this ancient volcano Mount Multnomah, Hodge theorized that it had collapsed to form a caldera just as Mount Mazama collapsed to form Crater Lake. In the 1940s, Howel Williams completed an analysis of the vicinity and concluded that Multnomah had never existed, instead demonstrating that each volcano in the area possessed its own individual eruptive history. Williams' 1944 paper, titled Volcanoes of the Three Sisters Region, Oregon Cascades, defined the basic outline of the region, though he lacked access to chemical techniques and radiometric dating. Oregon State University geologist and volcanologist Edward Taylor's analysis in 1978 determined that the current Broken Top cone was constructed on basaltic andesite lavas that built a platform. As dikes and sills invaded the edifice over time, it formed a volcanic cone made of different lavas including basaltic andesite, dacite, and rhyodacite, as well as tephra and pyroclastic materials from more explosive eruptions.