Layers of coarse Pleistocene gravel have been cored in the Cascadia Deep-Sea Channel up to 750 km along its course. Petrographic study indicates that the pebbles are lithologically similar to a number of rock types exposed along the Columbia River and its tributaries in Oregon and eastern Washington. The catastrophic late Pleistocene glacial floods which scoured this area of the Pacific Northwest transported coarse material derived from these outcrops down the river to the ocean. These catastrophic events are believed to have generated high-velocity and high-density turbidity currents which transported the coarse sediment for many hundreds of kilometers along the sea floor.