The Extent of the Cordilleran Ice-Sheet

Abstract

Through the courtesy of members of the United States Forest Service I was enabled, in the summer of 1912, to make some observations upon glaciation in the Kaniksu National Forest in northern Idaho. Because of the inaccessibility of a part of the region and the lack of suitable maps, the work was not complete; but in view of our slight knowledge of the extent and character of the continental glaciation in the northwestern United States, and because the nature of the country makes it extremely unlikely that it will be more carefully studied in the near future, it seems advisable to publish the facts noted. Moreover, there was discovered evidence of more complete reworking of glacial deposits by stream action than has yet been described. It is known that the front of the Cordilleran ice-sheet was marked by a series of marginal lobes occupying the north-south intermontane valleys of the northwestern United States. The line of crosses in Fig. i, based on data published by Professor Salisbury,' shows-the probable extent of some of these lobes. It is believed that the Pend d'Oreille lobe was continuous with that in the Colville valley, but its connection with the Kootenai lobe was well north of Bonners Ferry, and probably north of the International Boundary. In the paper cited nothing is said of the eastern boundary of the Pend d'Oreille lobe, but my observations show that the ice must have covered the divide between the Pend d'Oreille and Priest Lake valleys. This divide is a range of forest-covered hills having a maximum elevation of 6,500 feet, and an average height a thousand feet less. The former presence of ice on these hills is unmistakably shown by the rounded topography, by roches moutonnies, and by glacial striae-in one instance on bedrock, and in others on float. The striae on bedrock strike N..Io° W. Looking east across Priest