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Figure 23--On this east-west section at row 26 we begin to see a dramatic effect related to the gap in the mafic wedge. In this region, deep accretionary prism sedimentary rocks, as well as parts of underlying Crescent Fm. basement, are shoved northeastward into the gap. This effect is observed most clearly on this and the following three images (sections for rows 26-29). The prism is thickest in this region, related to a 'critical taper' effect where the JDF arch causes the dip of the JDF plate to be shallowest. The arch axis may be a point where the mantle wedge is split apart.