Its volcanic rocks remain undated, but the large amount of dissection and evidence of glacial ice overriding the volcano indicates that it formed more than 75,000 years ago before the Wisconsinan Glaciation. As a result, the rocks comprising Mount Fee do not display evidence of interaction with glacial ice; the duration of volcanic events is unknown, and the exact timing of eruptive events is unknown. However, a large variety of volcanoes formed subglacially between 25,000 and 10,000 years ago in the vicinity of Mount Fee, including the lava domes of Ember Ridge to the south. At least three phases of eruptive activity have been recognized at Mount Fee. The only exposed remnant of Fee's earliest volcanic activity is a minor outcrop of pyroclastic rock. This is evidence of explosive eruptions during Fee's eruptive history, as well as its first volcanic event. The second volcanic event produced a sequence of volcanic rocks on Fee's eastern flank. This volcanic material was likely deposited when a sequence of lava flows and broken lava fragments erupted from a volcanic vent and moved down the flanks during the construction of the ancestral Mount Fee. Following extensive dissection, renewed volcanism produced a viscous series of lavas on its northern flank. The U-shaped crevice separating the two main summits of Mount Fee separates this lava flow from the main volcanic ridge. The conduit from which these lava flows originated was likely vertical in structure and intruded through older rocks deposited during Fee's earlier volcanic events. This volcanic event was also followed by a period of erosion, and likely one or more glacial periods. Extensive erosion following the last volcanic event at Mount Fee has created the rugged north-south trending ridge that currently forms a prominent landmark. The dacite and rhyodacite rocks comprising Mount Fee contain up to 70% brown volcanic glass and up to 15% vesicles. About 25% of the rocks contain crystal content, including plagioclase, hornblende, orthopyroxene, orthoclase and sporadic quartz. The orthoclase crystals are interpreted to represent rock fragments that became enveloped during hardening of the dacitic lavas. A portion of the southwestern flank of Mount Fee comprises no volcanic glass, but rather composed of an abnormal cryptocrystalline matrix. This indicates that it might have developed as part of a subvolcanic intrusion. Human habitation at Mount Fee extends from hundreds to thousands of years ago. Glassy volcanic rocks, such as rhyodacite, were widely used to make knives, chisels, adzes and other sharp tools before the arrival of Europeans in the 18th century.