The second eruptive period consisted of explosive eruptions, which constructed scoria cones and lava flows to the south of Sheridan Mountain, known as the Siah Butte vents. These extend to the south end of the chain. The third period produced the shield volcano beneath Mount Bachelor out of basaltic andesite, later constructing its summit, in addition to a shield volcano that is topped by the Kwohl Butte. ʻAʻā lava erupted from Mount Bachelor during this third period coursed down its northern and northwestern sides. By 12,000 years ago, Mount Bachelor was close to its current size, as the oldest moraines from glaciers on the mountain (which are covered by lava flows from this third eruptive episode) can be dated to this time period. The current edifice at Mount Bachelor had been finished by about 10,000 years ago, followed by a gap in eruptive activity that lasted for 2,000 years. The latest eruptive activity within the chain yielded scoria cones and lava flows, including the Egan cone, which can be observed on Mount Bachelor's lower northern flank. Due to the presence of Mazama Ash on the northern side of the volcano, no eruptive activity is likely to have happened since 7,700 years ago.