Volcanic activity in the vicinity of Mount Jefferson tends to originate from either stratovolcanoes that erupt for thousands of years or monogenetic volcanoes, which only erupt for brief periods of time. At least 35 volcanic vents can be detected within of the main volcanic cone at Mount Jefferson. These have produced andesitic and dacitic lava flows, lava domes, small shield volcanoes, and lava aprons. Basalt lava flows, at least two of which are younger than 7,700 years old, have been produced from four monogenetic volcanoes to the south of Jefferson, and they are not directly related to activity at the Mount Jefferson volcano. Rhyodacitic lava flows and pyroclastic material, which have since been significantly altered and stripped by glaciation, originated from eight vents in the area. The Mount Jefferson vicinity contains at least 40 of the 190 documented lava domes in the Oregon Cascades, including the tall Goat's Peak dome; it also contains monogenetic tuyas (flat-topped, steep-sided volcanoes formed when lava erupts through a thick glacier or ice sheet) and emplacements of hyaloclastite among mafic lava flows.