The Channeled Scabland, Washington State, United States, is only partly the result of erosion by the catastrophic drainage of Glacial Lake Missoula: there were other sources of meltwater. Recent sedimentary investigations of some sites in the Missoula basin, and in the Channeled Scabland, support a single large late Wisconsin flood, as opposed to multiple floods proposed for this time period. Sediment in the Glacial Lake Missoula basin records rapid infill by jökulhlaups draining into Lake Missoula from upstream, punctuating a long period of normal varve sedimentation. This was independent of sedimentation in the main Scabland tract, where proximal and distal rhythmic beds are explained as resulting from multiple pulses, or surges, within a single flood. Geomorphic and sedimentary evidence supports the conclusion that drainage from the Cordilleran trunk valleys was important, and pulses were probably related to the drainage of these valleys.