Geology Reference
In-Depth Information
Map of floods from ice-dammed glacial Lake Missoula (black) showing branching structure of flood through the
Channeled Scablands and the extent of backwater up into the Willamette Valley (gray).
The next summer, Bretz went back to the field and found deposits formed by water flow-
ing backwards up Columbia River tributaries. Along the Snake River he traced backwater
deposits upstream beyond Lewiston, Idaho. Only a huge flood could have sent deep water
surging back up into tributaries. Grudgingly taking Pardee's hint, Bretz settled on drainage
from Lake Missoula as the source of his flood.
Nobody else believed him. The remoteness of the scablands and the difficulty of trav-
eling there during the Depression fostered skepticism among colleagues back east, few of
whom had been out west to see the area for themselves.
Geologists kept arguing about the scablands and attacking the heretic's flood. One col-
league dusted off Bretz's original idea of a flood produced by water backing up from a
Columbia River ice jam. Others invoked glacial erosion, ignoring the fact that the scab-
