The Boring Lava Field is a Plio-Pleistocene volcanic field with cinder cones, small shield volcanoes, and lava flows in the northern Willamette Valley of the U.S. state of Oregon and adjacent southwest Washington state. The zone became active about 2.7 million years ago, with long periods of eruptive activity interspersed with quiescence. Its last eruptions took place about 57,000 years ago; individual volcanic vents are considered extinct, but the field itself is not. The volcanic field covers an area of about 1,500 square miles (3,900 km2) and has a total volume of 2.4 cubic miles (10 km3). The highest elevation of the field is at Larch Mountain, which reaches a height of 4,055 feet (1,236 m). The Portland metropolitan area, including suburbs, is one of the few places in the continental United States to have extinct volcanoes within a city's limits. The probability of future eruptions affecting the Portland metropolitan area is very low. (Full article...)