OCT., 1899.] 



YELLOW PINE BELT. 



31 



of the Transition zone. On the cooler and liigher canyon sloi)es and 

 adjacent foothills the pouderosa pines continue to tlie border of the 

 Sacramento Yalley. 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 

 occur in greater or less abundance in the valleys of liussian Creek, 

 North aiul South forks of Salmon liiver, Trinity Eiver, and Klamath 

 River, and at appropriate altitudes on the west arm of Salmon Moun- 

 tains, Trinity Mountains, and the mountains between Hoopa Valley 

 and Redwood Creek. Hence the Shasta forest of ponderosa pines is 



Flu. ]'j. — Maii/.aiiita cliaparial cm sciiitli .slnpf, iil' Shasta. 



directly continuous — either broadly or by narrow and tortuous tongues — 

 with corresponding forests of southern Oregon, northeastern Califor- 

 nia, northwestern California, and the tlanks of the Sierra. 



The ponderosa pines of the Shasta plateau and adjacent region are 

 peculiar — peculiar in the extent of their variability — and deserve care- 

 ful study. Not only do the cones of adjacent trees ]n'esent an unusual 

 degree of variation in size and compactness (particularly noticeable in 

 Scott A'alley), 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 

 Pin u fi Jeffrey i grows within a short distance oi ponderosa. Whether or 



