 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.