Plinth Peak, sometimes called Plinth Mountain, is the highest satellite cone of Mount Meager, and one of four overlapping volcanic cones which together form the northermost volcanic complex in the Cascade Volcanic Arc and the Garibaldi Volcanic Belt. It is the youngest vent, which last erupted about 2350 years ago.
Plinth Peak is the most recent volcanic peak of Mount Meager to erupt, and the most recent in the Garibaldi Volcanic Belt. The eruption was similar to the 1980 eruption of Mount St. Helens and sent ash as far as southern Alberta and dammed the Lillooet River, forming Keyhole Falls. The steep north face of the peak is the remnant of the inner crater wall, which was destroyed by the eruption.