664 OREGON AND NORTHERN CALIFORNIA. 
latter was properly part of the bank of the river, as the usual height 
of the bank in that vicinity is twenty feet, and at this part it was only 
twelve feet. ‘These small terraces were common in the lower prairie ; 
in figure 6 at N there is one of five feet. They disappear after con- 
tinuing on a mile or two, and at times commence again at different 
distances from the river. 
The day following we left the lower prairie again, by ascending 
first a terrace of twenty feet, and half a mile back, another steep slope 
of eighty feet, making the whole ascent to the upper prairie one hun- 
dred feet. It was a region of hills of nearly uniform height, but very 
gradually rising back to two hundred feet. The hills were usually 
rounded ; but in occasional sections they were found to consist of hori- 
zontal beds of clayey and sandy loam, gravel and pebbles, proving them 
to be alluvial, of which, however, there could be no doubt, judging 
from their situation and general features. In the course of ten hours’ 
riding we descended again to the bottom-land of the Sacramento. The 
upper alluvial region here faced the lower prairie with a line of steep 
fronts seventy to one hundred feet high; and half a mile below, they 
bordered the river in a bluff of one hundred feet (figure 7). 
In the bluff of one hundred feet, just alluded to, the lower portions 
of the alluvium consisted of a sandy loam, while the upper were 
beds of gravel and pebbles. ‘The layers were several feet thick, and 
did not appear to be subdivided into thin lamine or layers of depo- 
sition. ‘They were slightly consolidated into an argillaceous sand- 
stone, and this half-formed rock was occasionally hard enough to fall 
to the bottom in compact masses ten to twenty cubic feet in size: the 
lower layer projects into the river, and forms a platform much eroded 
by the current. 
The following day, in latitude 404°, we ascended again to the 
upper prairie, which in this part was less broken, being mostly an 
undulating plain. Descending at one place, we found a slope of 
thirty-five feet (M, fig. 8), and three hundred yards beyond (at N, fig. 
8), a second terrace of twenty-five feet; two hundred yards from here, 
the river lay between banks twenty feet high. 
We forded the Sacramento to its east bank, about forty miles from 
where we first made the alluvial region, and travelled for the re- 
mainder of the way, till we took boats, on the lower prairie. We 
approached the upper prairie in but one instance; and at this place it 
was fifty feet high, and was as pebbly as the same plain on the other 
side of the river. A trace of the upper prairie is found on the 
