THE NORTHERN PACIFIC ROUTE. 
on the right (west). 
167 
This cliff is about 150 feet high and in the lower 
part shows beautiful columnar structure (see PI. 
Mesa. 
cderem 687 feet. 
Populat. 
St. Peat 1 625 miles. 
XXII, B), but the columns are small, and they may 
not be visible from the train. The rugged walls con- 
oe as far as Mesa, but beyond that station the val- 
opens and the walls are lower and have lost much 
of their rugged shavastbe: 
poured forth. The eruptions were accom- 
panied by explosions, which produced 
large quantities of tuff, volcanic ash, and 
pumice. While the volcanic eruptions 
what uplifted, and the streams, made more 
powerful by the increase in grade due to 
the uplift, carried vast quantities of the 
andesitic material eastward to the lake 
basin previously described. In thisbody 
of fresh water the waste material was de- 
posited as mud, sand, or gravel, together 
with some sheets of basaltic lava that 
apparently marked the last expiring gasp 
of the giant forces which had previously 
poured forth such 
In the Yakima Valley the beds 
thus laid down have been named th 
Ellensburg formation. Here the sedi- 
ments are coarse, indicating nearness to 
the margin of the lake and to the source of 
supply, reg farther out in the basin, ac- 
. ©. Russell, the material 
nas in this lake is largely white silt, 
composed chiefly of volcanic dust and ash 
that were blown out of the new set of 
volcanoes which then were active to the 
west. This material is exceedingly fine 
and forms the White Bluff on Columbia 
River some distance above Pasco (PI. 
ag A) and the isolated hills at Fish- 
“Tp to the close of the lake period of cen- 
tral Washington the Cascade Range, as it 
- known to-day, did not exist. During 
7 area now occupied by the 
eg worn down by streams, and finally 
it reached that state of low relief that is 
was then 
_ Shomabs eee aan 3% ee 
The oe uplift of the Cascade Range 
tyes opel’ 
ee or the opening chapter in at Qua- 
rnary. These mountains not 
portent by a volcanic outburst, "Mesa 
ee events were of common occurrence 
n this country, but they are the result of 
a peta uplift of this part of the earth’s 
crust, which produced a great arched pla- 
teau about 5,000 feet above sea level. 
Volcanic activity was not entirely sus- 
pended in this region, and here and there 
vents were formed from which poured 
forth lava and volcanic ash, and large 
cones were built upon the surface of the - 
deeply eroded plateau. These are the 
great conical which are such ma- 
jestic features of the Cascade Range. 
The next great epoch in the geologic 
ogan (o-kan-og’an) River and then across 
the immediate canyon of eo Columbia_ 
That great river in this Sa of flood was 
temporarily divert 
lee City, but on the retreat of the ice 5 it 
resumed its original channel. The great 
cold of the wlacial epoch left large parts of 
this region without a cover of vegetation, 
and much of the soft material laid down 
