146 fF. M. ANDERSON 
the region, probably representing two or more periods of 
revolution. 
The two systems of ranges cross each other nearly at right 
angles. The most conspicuous ranges, among which are the 
Rogue River, Siskiyou, Scott, and Trinity mountains, have a 
westerly, or south of westerly trend, while the Yallo Bally, Bally 
Choop, South Fork, and Salmon River Mountains, and many of 
the less important spurs and ridges approximate a more north- 
erly or northwesterly course. The fold represented in the Sal- 
mon River range particularly can be followed from the Trinity 
basin nearly continuously northward to the Rogue River Moun- 
tains, crossing perhaps all of the ranges running toward the 
coast. Of the east and west ranges it should be noticed that 
while all of them apparently terminate in the vicinity of the 
Cascades, this termination, for two of them at least, is more 
apparent than real. The east and west axis, for example, that is 
represented by the Rogue River Mountains crosses the Cascade 
range near Mount Thielsen and continues in a north of easterly 
direction through eastern Oregon toward the equally old cluster 
of the Blue Mountains, and forms a broad though high divide 
between the drainage of the Klamath Lakes and the Deschutes 
and Crooked rivers, flowing toward the Columbia. 
In a similar manner the high range traversing northern 
California in almost a parallel direction, along the southern bor- 
der of Siskiyou county, has an eastern projection which crosses 
the Cascades in the vicinity of Mt. Shasta and forms a high 
divide which separates the drainage of the Klamath Lakes and 
river from that of Pitt River and the Sacramento. Midway 
between these two folds is the Siskiyou range, almost parallel to 
the others, but not traceable beyond the Cascades. On either 
side of the Siskiyou range are the valleys of Rogue River and 
the Klamath. Each of the three ranges contains old crystalline 
‘rocks, including granites, gabbros, and peridotites, whose age 
undoubtedly antedates the later Cretaceous rocks to be described 
presently. While it is not clear that these crystalline elements 
have any direct bearing upon the question, it cannot be denied 
