This article: North Sister, also known as "Faith", is the oldest and most highly eroded of the three, with zigzagging rock pinnacles between glaciers. It is a shield volcano that overlays a more ancient shield volcano named Little Brother. North Sister is 5 miles (8 km) wide, and its summit elevation is 10,090 feet (3,075 m). Consisting primarily of basaltic andesite, it has a more mafic composition than the other two volcanoes. Its deposits are rich in palagonite and red and black cinders, and they are progressively more iron-rich the younger they are. North Sister's lava flows demonstrate similar compositions throughout the mountain's long eruptive history. The oldest lava flows on North Sister have been dated to roughly 311,000 years ago, though the oldest reliably dated deposits are approximately 119,000 years old. Estimates place the volcano's last eruption at 46,000 years ago, in the Late Pleistocene.North Sister possesses more dikes than any similar Cascade peak, caused by lava intruding into pre-existing rocks. Many of these dikes were pushed aside by the intrusion of a 980-foot (300 m)-wide volcanic plug. The dikes and plug were exposed by centuries of erosion.   At one point, the volcano stood more than 11,000 feet (3,400 m) high, but erosion reduced this volume by a quarter to a third. The plug is now exposed and forms North Sister's summits at Prouty Peak and the South Horn. contains an answer for the question: When does estimates place Faith's last eruption?, what is it ?


46,000 years ago