PHYVSIOGRAPAY OF KLAMATH MOUNTAINS 149 
As will be shown later, Shasta and Rogue River valleys are easily 
united, while the latter may be followed westward, toward and 
into a somewhat close connection with the valley of the Illinois 
River. On the other hand, the valleys of the Trinity basin may 
be linked together, connecting on the east with the valley of the 
Sacramento through a low divide between important ranges. 
Looking westward from the Sacramento valley in the neighbor- 
hood of Red Bluff one sees a low depression, separating what 
otherwise appears to be a continuous range of mountains border- 
ing the Great Valley along the west. This depression is a 
low divide leading into the Trinity basin between the Yallo 
Bally and Bally Choop ranges. Beginning at this point a broadly 
curved line may be drawn in a northwesterly direction down the 
valley of a southern tributary of the Trinity, including the Hay 
Fork, Hyampom, South Fork, and Hoopa valleys, and extending 
to the mouth of the Klamath River. A little farther to the north 
a similar line may be drawn along the course of the main Trinity 
River, which merges into the former at the junction of the South 
Fork and the main branch of the Trinity. The two are included 
in what is here called the Trinity basin, which probably should 
be regarded as the southern limit of the Klamath Mountains, 
unless a purely geological or lithological basis of definition is to 
be employed, in which case they should be extended southward 
nearly, if not quite, to the Bay of San Francisco. 
Type of valleys—A peculiarity of all the intermontane val- 
leys of the Klamath system is the manner of their drainage. 
Almost without exception their outlets cross one or more 
ranges through a narrow gorge or canyon. Shasta valley, for 
example, lying on the eastern flank of the older mountains, is 
drained, in common with the valley of the Klamath Lakes, by the 
Klamath River, which traverses a broad stretch of mountainous 
country to the westward for nearly one hundred miles before it 
emerges into the broader valley near its mouth. In its course 
it crosses the axis of the Salmon River range and other smaller 
ranges, through which its valley is reduced to the character of a 
gorge. And these valley-basins sometimes contrast rather 
