568 Part IV. Chapter 3. 
to the fact that the moisture-laden winds of the Pacific are cut off by the 
Cascade range of mountains. The eastern limit of this plain is the western 
base of the Bitterroot Mountains toward the north, while the Rocky 
Mountains form the eastern boundary in the south. 
Thus a great wedge-shaped area is formed, its base continuous with the 
deserts of Nevada and its apex in the north surrounded by the forest which 
connects the northern end of the Bitterroot Mountains with the northern end 
of the Cascades. The southern boundary of this district is marked by 
STEIN’S Mountains, Goose Lake and Upper Klamath Lake in extreme southern 
Oregon. The absence of Larrea mexicana (the creosote bush), various 
Cactaceae delimits these deserts from those of southern Arizona. 
Sage brush Formation. The vegetation of this district consists principally 
of sage brush Artemisia tridentata, which covers the country away from the 
streams with a gray mantle and constitutes probably nine tenths ofthe 
vegetation. Here there is never a sod except in favorable localities along 
streams where the sedges and native clovers abound. The grasses of many 
species are all bunch grasses and the clumps are invariably separated by inter- 
vals of a few inches to several feet. The entire absence of buffalo grass 
Buchloe dactyloides and grama grass Bouteloua oligostachya is noteworthy. There 
are many annual plants and growing with them are tuberous rooted 
perennials which have stored up during the preceding year’s growth a large 
amount of reserve food. 
In the lower portions of all the basin, as well, as in poorly drained areas 
along the river bottoms, are situated intensely alkaline areas which support 
no vegetation whatever and are known locally as “sleek deserts”. 
A few trees occur in this desert. Pinus albicaulis makes a scanty growth 
at highest elevations on Pine Forest range. STEIN’s Mountains have no pines, 
but Funiperus virginiana is quite abundant. Pinus ponderosa var. scopulorum, 
the bull pine, occurs in the spurs of the Blue Mountains. Aside from the 
pines and juniper the only trees of the district are Populus tremuloides, RB 
trichocarpa. Among the shrubby plants which form dense thickets, often 
over areas of considerable extent, may be mentioned: Cercocarpus ledifolius, 
Amelanchier alnifolia, Ceanothus velutinus, Holodiscus dumosus, Symphoricarpos 
‚ oreophilus, Potentilla fruticosa, Prunus emarginata, P. demissa (Chaparra 
Formation). Along the moister gulches one always finds a profuse growth 
of willows which are also sometimes found forming thickets on high, moist, 
shady slopes. Extensive growth of alder are also found in the same loca- 
lities *) 
The yellow pine belt in eastern Washington lies between the altitudes 1,800 an and 
3,300 feet (550 and 1000 meters). In places Pinus ponderosa descends nearly to sea level, 
as along the Columbia River, but it shows a marked predilection for soils of granitic origin 
Where pure the forests of this tree are open in character \and marked by a relatively small 
amount Of forest litter. There is a scattered growth of various shrubs such as Physocarpus 
}) See GRIFFITHS, DAvıD: see Bibliography p. 76. 
Birk 
