578 RALPH W. CHANEY 



for valuable advice and assistance in determining species, and to 

 Dr. H. C. Cowles, of the University of Chicago, for his direction in 

 the interpretation of the ecological data. The work during the 

 season of 19 17 was carried on with the aid of a grant from the 

 Research Fund of the American Association for the Advancement 

 of Science, to which organization sincere acknowledgment is due. 



GEOGRAPHIC LOCATION AND TOPOGRAPHIC FEATURES OF THE 

 COLUMBIA GORGE 



The gorge of the Columbia River is that portion of its valley 

 in the Cascade Range. Its general features are shown in the 

 Mt. Hood sheet of the United States Geological Survey, where the 

 Columbia River forms the boundary between Oregon and Wash- 

 ington. The river has exposed here a section which has a maximum 

 thickness of over 4,000 feet. The basal Eagle Creek formation is 

 displayed at the axis of the range, giving the most complete section 

 just west of the boundary between Multnomah and Hood River 

 counties. The total length of the gorge from Troutdale, Oregon, 

 on the west to The Dalles, Oregon, on the east is about 70 miles. 

 Its width averages about one mile. 



The walls of the gorge rise steeply, especially on the Oregon side, 

 where cliffs of basalt rise more than 2,000 feet almost vertically. 

 A number of peaks, some of them representing volcanic cones, lie 

 a short distance back from the edge of the walls. Larch Moun- 

 tain, 4,045 feet, and Mt. Defiance, 4,960 feet, are conspicuous 

 examples. Numerous small tributary streams flow into the 

 Columbia from each side through canyons which are much shallower 

 than that of the master-stream. As a result each has at or near 

 its mouth a falls or series of falls, the highest being Multnomah 

 Falls, 620 feet high, at the mouth of Multnomah Creek. The 

 sections exposed in the lower stretches of these tributaries add much 

 to our knowledge of the stratigraphy and fossil content of the rocks. 



The western two-thirds of the gorge is occupied by the luxuriant 

 forest of Douglas spruce so characteristic of the Pacific coast. 

 Much of the geologic record is hidden by the density of this forest 

 and its undergrowth. The best accessible sections are found where 

 the building of roads and trails has temporarily destroyed the 



