HIGH-LEVEL TERRACES OF OKANOGAN VALLEY, 
WASHINGTON. 
CHARLES KEYES. 
Recent observations in the interior of Washington state in- 
dicate in no unmistakable terms that in late geological times the 
entire drainage of the region has repeatedly undergone great 
vicissitudes. Its juvenile lines have been profoundly disturbed, 
displaced, and variously modified. By floods of lava on the one 
hand and on the other hand by advancing glaciers the original 
river courses have been completely lost to view. A notable and 
concrete illustration is the Big Bend of the Columbia river— that 
stretch of the great stream nearly 200 miles long lying between 1 
the mouths of the Spokane and Snake rivers. 
This wide diversion of the course of the Columbia river in 
central, Washington is the result of prodigious lava flows which 
have pushed out northwestward from the great Idaho volcanic 
fields. In glacial times immense ice tongues have advanced from 
the main Canadian mass into the Columbia canyon, effectually 
blocking the flow of the river and forming extensive lakes. An 
old outlet of the main lake is seen in the Grand Coulee now a 
long dry canyon deeply intrenched in the lava field and entirely 
crossing Douglass county. 
In brief the region under consideration is one in which a pene- 
plained surface has been broadly uplifted, deeply dissected, 
greatly eroded by overriding glaciers, and now is again subject 
to normal river corrasion. Few districts display to better ad- 
vantage the effects of the '.profound erosive power of glacier move- 
ments. Although the glaciers had the 'old river valleys to guide 
them they have deepened some of them until the bottom of Lake 
Chelan basin, for instance, now lies several hundreds of feet be- 
low sea-level. 
A conspicuous feature of the present river valley is the re- 
markable series of high-level terraces which their sides present. 
These embankments persist at various heights above the water- 
level up to 700 or 800 feet. They are manifestly of diverse 
origins. An old river terrace and an old lake beach attract 
principal attention. The first of these was formed by greatly 
