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 1917 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 
