The Wrangell Volcanic Field is a volcanic field stretching from eastern Alaska in the United States to the southwestern Yukon Territory in Canada. The field includes the four highest volcanoes in the United States, Mount Bona, Mount Blackburn, Mount Sanford, and Mount Churchill, all of which exceed 15,000 ft (4,600 m) in elevation. It formed as a result of subduction of the Pacific Plate beneath the North American Plate at the easternmost end of the Aleutian Trench. The bulk of the Wrangell Volcanic Field lies within the Wrangell Mountains of Alaska, but the field also extends eastwards into the neighboring Saint Elias Mountains and the Yukon Territory. The east-west length of the field is over 200 mile (320 km), while the width reaches up to 80 miles (130 km) in the central Wrangell Mountains. The field includes numerous shield volcanoes, stratovolcanoes, caldera complexes, cinder cones, and extensive lava flows, which have erupted throughout the past 26 million years. All of the higher peaks are less than 5 million years old, since the rate of glacial erosion is very high in this region of extreme snowfall and cold temperatures. Higher elevations of the field above 5,000 ft (1,500 m) are almost entirely covered in glaciers and icefields, especially on the windward southern side of the ranges. The field is named for Mount Wrangell, a massive shield volcano which has been active historically. The stratovolcano of Mount Churchill has had the largest recent eruptions, with two large-magnitude explosive eruptions in the last 2,000 years that blanketed most of the Yukon with volcanic ash (the White River Ash). The volcanoes of the western Wrangell Mountains are less than 5 million years old with the youngest lava flows are probably as young as 50,000 years ago. The Canadian portion of the field is dominated by scattered remnants of upper Cenozoic subaerial lavas and pyroclastic rocks. Over large areas extrusive rocks lie in flat undisturbed piles on a Cenozoic surface of moderate relief. Locally, however, strata of the same age have been affected by a late pulse of tectonism, during which they were faulted, contorted into tight symmetrical folds, or overridden by pre-Cenozoic baserocks along southwesterly dipping thrust faults. Considerable recent uplift, accompanied by rapid erosion, has reduced once vast areas of upper Cenozoic volcanic rocks to small isolated remnants. Although no centers younger than late Miocene are known in Canada, the eruption of rhyolite