RIVER TERRACES. 661 
Willammet, the river here running in rapids, between steep alluvial 
banks twenty-five feet high. In the course of a mile along the river, 
the terrace neared the banks to within a few rods. Its height was 
still about sixty feet. We forded the river two miles beyond, and on 
the opposite side found the terrace again of the same height, about 
a quarter of a mile back from the river. 
This terrace is described by the settlers, as characterizing the 
alluvial plains throughout the Willammet District. It is generally 
within one or two miles of the river, but retreats at times four or five 
miles, and in other parts borders the stream. The upper plain is 
occasionally fifteen miles wide, but the ordinary breadth is less than 
four miles. The slope between the upper and lower prairies is 
usually inclined at an angle of thirty degrees, and in most places it is 
densely overgrown with trees and shrubbery. High rolling prairie 
hills bound the alluvial district, and occasionally a hill stands isolated 
in the plains. 
The sections of the lower plain, exposed along the banks of the 
stream, present successive deposits of a grayish, friable loam, and 
pebbly or gravelly layers. The lower five feet usually consist of 
stones and pebbles, while the upper twenty are mostly a sandy loam. 
I observed no good section of the upper plain, and therefore can add 
nothing to the statements respecting the surface, on page 619. 
Willammet Plains and Country south to San Francisco.—On the 
trip to California, we did not see the Willammet again after leaving 
the Mission Settlement, allhough we were traversing its prairies, till 
we reached the Elk Mountains. Passing a region of hills on the first 
day out, we came upon the upper prairie, and shortly after descended 
fifty feet to the lower; from which, in less than a mile, we ascended 
again the same slope. 
On a small rivulet, we found the upper and lower flats to differ 
twenty feet in height. 
On another small stream, a few yards wide, about nineteen miles 
from the settlement, there was a similar upper and lower flat, twenty 
feet apart. 
Twenty-five miles beyond, after six miles of flat prairie, there was 
another streamlet, not knee deep, called Marsh Creek, with fifteen feet 
between the height of the upper and lower plains bordering it. 
Sixty-five miles from the Mission Settlement, Lumtumbuf Creek, 
another small affluent to the Willammet, is bordered in some parts by 
a lower prairie lying ten feet below the upper, and fifteen above the 
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