More recent volcanic activity has created a northwest trending line of volcanic rocks called the Wrangell Volcanic Belt. This volcanic belt lies largely in the U.S. state of Alaska, but extends across the Alaska-Yukon border into southwestern Yukon where it contains scattered remnants of subaerial lavas and pyroclastic rocks which are preserved along the entire eastern fringe of the ice covered Saint Elias Mountains. The Wrangell Volcanic Belt formed as a result of arc volcanism related to subduction of the Pacific Plate under the northern portion of the North American Plate. Over large areas extrusive rocks lie in flat undisturbed piles on a Tertiary 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-Tertiary basement rocks along southwesterly dipping thrust faults. Considerable recent uplift, accompanied by rapid erosion, has reduced once vast areas of upper Tertiary volcanic rocks to small isolated remnants. Although no eruptions have occurred in the Yukon portion of the Wrangell Belt for the past five million years, two large (VEI-6) explosive eruptions from Mount Churchill west of the Alaska-Yukon border, created the White River Ash deposit. This volcanic ash deposit is estimated 1,890 and 1,250 years old, covering more than of northwestern Canada and adjacent eastern Alaska. Unproven legends from indigenous people in the area indicate the final eruption from Mount Churchill 1,250 years ago disrupted food supplies and forced them to move further south.