Development of a late Quaternary marine terraced landscape during on-goingtectonic contraction, Crescent City coastal plain, California

The Crescent City coastal plain is a low-lying surface of negligible relief that lies on the upper plate of the Cascadia subduction zone in northernmo st California. Whereas coastal reaches to the north in southern Oregon and to the south near Cape Mendocino contain flights of deformed marine terrace s from which a neotectonic history can be deduced, equivalent terraces on t he Crescent City coastal plain are not as pronounced. Reexamination of the coastal plain revealed three late Pleistocene marine terraces, identified o n the basis of subtle geomorphic boundaries and further delineated by diffe rentiable degrees of soil development. The youngest marine terrace is prese rved in the axial valley of a broad syncline, and the two older marine terr aces face each other across the axial region. An active thrust fault, previ ously recognized offshore, underlies the coastal plain, and folding in the hanging wall of this thrust fault has dictated, through differential uplift , the depositional limits of each successive marine terrace unit. This stud y demonstrates the importance of local structures in coastal landscape evol ution along tectonically active coastlines and exemplifies the utility of s oil relative-age determinations to identify actively growing folds in lands capes of low relief, (C) 1999 University of Washington.