Seismic reflection data show that highly reflective rocks make up the midcrust of the convergent margin adjacent to the eastern Aleutian Trench. These rocks form an arch that strikes obliquely across the strongly expressed NE-SW structural grain of exposed Mesozoic rocks. Deep reflections could be from underplated rocks that have been arched by the imbrication or underplating of strata below the reflective rocks. Speculates that one band of reflections that rises toward but does not reach the surface is from the Eagle River thrust fault, which separates Late Cretaceous melange from deformed turbidite sequences of the same age. -from Authors