OCT., 1899. } YELLOW PINE BELT. 31 
of the Transition zone. On the cooler and higher canyon slopes and 
adjacent foothills the ponderosa pines continue to the border of the 
Sacramento Valley. West of Shasta they cover all but the highest 
elevations of the Scott Mountains, completely surround Scott Valley, 
and reach up a considerable distance over the east arm of the Salmon 
Mountains, where, mixed as usual with Douglas firs, incense cedars, 
and sugar pines, they fill the Transition zone. Still farther west they 
oceur in greater or less abundance in the valleys of Russian Creek, 
North and South forks of Saimon River, Trinity River, and Klamath 
River, and at appropriate altitudes on the west arm of Salmon Moun- 
tains, Trinity Mountains, and the mountains between Hoopa Valley 
and hedwood Creek. Hence the Shasta forest of ponderosa pines is 
| 
Fic. 15.—Manzanita chaparral on south slope of Shasta. 
directly continuous—either broadly or by narrow and tortuous tongues— 
with corresponding forests of southern Oregon, northeastern Califor- 
nia, northwestern California, and the flanks of the Sierra. 
The ponderosa pines of the Shasta plateau and adjacent region are 
peculiar—peculiar in the extent of their variability—aud deserve care- 
ful study. Not only do the cones of adjacent trees present an unusual 
degree of variation in size and compactness (particularly noticeable in 
Scott Valley), but the cones of trees subjected to apparently slight 
differences of temperature, moisture, and soil present certain average 
differences that are quite surprising. Moreover, on higher parts of 
the Scott Mountains, and also along their cool east base, fairly typical 
Pinus jeffreyi grows within a short distance of ponderosa. Whether or 
