TOPOGRAPHY AND LIFE ZONES OF OREGON [33] 



recently published extensive lists of plants and animals characteristic of 

 the life zones of the State, so that it seems useless to repeat them here in 

 detail. Only a few of the more prominent and characteristic zonal indi- 

 cators are listed, therefore, in the following discussion of the different 

 zones. 



UPPER SONORAN ZONE 



OF THE life zones present in Oregon, the Upper Sonoran is the first in the 

 order presented above. The valleys of the Columbia and the Snake Rivers 

 and the tongues of varying width and length along their tributaries are 

 Upper Sonoran; likewise, that part (approximately half) of the great sage 

 plateau that lies at an altitude of 4,500 feet or less. On cold northern 

 exposures the upper edge of this zone may drop down to 3, 500 feet or less 

 and on hot dry southern slopes it may rise to 5,000 feet or more as tongues 

 or islands surrounded by the Transition or even the Canadian Zones. 

 West of the Cascades the upper valley of the Rogue River, particularly 

 the flat lands and foothills about Medford and as far down the river as 

 Hells Canyon below Grants Pass, and the valley of the Umpqua in the 

 vicinity of Roseburg are both in this zone. The farthest northward exten- 

 sions recognizable are along the Willamette River north of Eugene, where 

 several patches of almost typical Upper Sonoran vegetation are to be 

 found. 



Specialists in ecology, as in other lines of scientific research, tend to 

 draw finer and finer distinctions and break such concepts as the life zones 

 into successively smaller and less recognizable units. Like some of our 

 ultramodern subspecies of birds and mammals, they are unrecognizable 

 without reference to notes and locality labels. Following this idea, the 

 Upper Sonoran, which in itself is the arid subdivision of the Austral Zone, 

 is again divided into extreme arid and semiarid zones as they apply to 

 our State, and each of these in turn is capable of being still further divided, 

 again and again. 



Without considering these further, in the semiarid section of the Upper 

 Sonoran that covers the Rogue and Umpqua sections of western Oregon 

 are found certain plants that most conspicuously characterize this area. 

 Some of these are the California lilacs (Ceanothus cuneatus, C. integerrimus, 

 and C. sanguineus), manzanita (^Arctosta-phylos viscida), a tiny mariposa 

 (Calochortus uniflorus^) y birchleaf mahogany (Cercocarpus betulaefolms), soap- 

 root (Chorogalum Corner tdianum)^ a rabbi tbrush (Chrysothamnus nauseosus^), a 

 false buckwheat (Eriogonum nudum) growing two feet or more tall, alfi- 

 leria (Erodtum cicutarium), the striking red bells (Fritillaria recurva), two 

 brodiaeas (Brodiaea cafitata and B. hendersoni), bitterbush (Purshia triden- 

 tata), white pentstemon (Pentstemon deustus), a wild iris (Iris chrysophylla), 

 chokecherry (Prunus demissa), and tasselbush (Garry a fremontt). 



Among the characteristic mammals are the California jack rabbit (Lepus 



