Mount Fee is a volcanic peak in the Pacific Ranges of the Coast Mountains in southwestern British Columbia, Canada. It is located 13 km (8.1 mi) south of Callaghan Lake and 21 km (13 mi) west of the resort town of Whistler. With a summit elevation of 2,162 m (7,093 ft) and a topographic prominence of 312 m (1,024 ft), it rises above the surrounding rugged landscape on an alpine mountain ridge. This mountain ridge represents the base of a north-south trending volcanic Field which Mount Fee occupies.
The mountain consists of a narrow north-south trending ridge of fine-grained volcanic rock and small amounts of fragmental material. It is 1.5 km (0.93 mi) long and 0.5 km (0.31 mi) wide with nearly vertical flanks. Mount Fee has two main summits, the southern tower of which is the highest. The summits are separated by a U-shaped crevice that gives them a prominent appearance.
Mount Fee is one of the southernmost volcanoes in the Mount Cayley volcanic field. This volcanic zone forms the central portion of the larger Garibaldi Volcanic Belt, which extends from the Silverthrone Caldera in the north to the Watts Point volcano in the south. The volcanic belt has formed as a result of ongoing subduction of the Juan de Fuca Plate under the North American Plate at the Cascadia subduction zone along the British Columbia Coast. This is a north-south trending fault zone about 1,000 km (620 mi) long, extending 80 km (50 mi) off the Pacific Northwest from Northern California to southwestern British Columbia. The plates move at a relative rate of over 10 mm (0.39 in) per year at an oblique angle to the subduction zone.
The edifice of Mount Fee is the remains of a volcanic feature that has been significantly eroded by glacial ice. It likely represents a dissected stratovolcano (also known as a composite volcano) that was larger in area and higher in elevation than its current form. Stratovolcanoes can reach heights of 2,500 m (8,000 ft) and consist of alternating layers of lava flows, volcanic ash, cinders, blocks and bombs. During the glacial periods, much of The Volcano's original outer cone of pyroclastic material was eroded away by moving layers of ice and rock.
The removal of the ejected volcanic material has exposed the dacite lava that forms the narrow north-south trending ridge of Mount Fee. Black Tusk, a pinnacle of dark volcanic rock to the southeast, is also interpreted to be the remains of a deeply eroded volcano that was once covered with pyroclastic material. The present day edifice of Mount Fee contains several lava spines that reach heights of 100 m (330 ft) to 150 m (490 ft) above the main ridge.
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.