The existence of four different interpretations of that extraordinary assemblage of erosional and depositional land forms of eastern Washington, the Channeled Scabland, indicates that rigorously definitive diagnostic characters had not been found. This study, dealing with new data, largely from extensive excavations and detailed topographic maps made by the U. S. Bureau of Reclamation in developing the great Columbia Basin Irrigation Project, returns to the earliest of the four interpretations: that channeled scabland is almost wholly the consequence of catastrophic flooding of glacial water across this part of the Columbia Plateau which remade preglacial valleys into an anastomosing complex of great river channels with huge cataracts, deep rock basins, and bars attaining magnitudes unknown elsewhere on earth.

The new evidence is held to establish firmly the following points:

  • (1) Some structural basins of the region did not have exterior drainage prior to arrival of glacial water.

  • (2) The gravel hills called bars by Bretz (1928a) have the shapes, surface markings, structures, and topographic situations possible only for subfluvial constructional deposits. In magnitudes and bouldery composition, they are sui generis.

  • (3) Several episodes of catastrophic discharge have occurred across this part of the Columbia Plateau.

  • (4) The Columbia Valley skirting the plateau has had comparable floods in which the scabland complex did not share.

  • (5) Successive floods have been differentiated only by topographic relations of their records, not by differential weathering and erosion.

  • (6) Bretz did not overestimate the magnitude of the erosion by glacial waters.

  • (7) The existing scabland features contradict the three later interpretations.

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