Compression of flat-lying Cascadia Basin (continental rise) sediment against the Washington continental slope, resulting from underthrusting of the Gorda–Juan de Fuca plate beneath the North American plate, progresses from passive uplift and anticlinal upwarping to thrust faulting. When folding and thrusting at the continental slope-rise boundary can no longer accommodate the rate of compression, the locus of deformation shifts offshore and a new anticline begins to form. Repetition of this deformational cycle has produced the multiple ridges of the lower continental slope and westward progradation of the continental margin. The most recent anticlinal upwarping apparently began 0.11 to 0.35 m.y. ago. Consolidation of the ridge sediment during the deformation process may be tectonically induced.

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