48 CONTRIBUTIONS FROM THE NATIONAL HERBARIUM. 
sions. The lower subdivision is grass-covered and lies immediately 
above the zone of the sagebrush. The conspicuously abundant plants 
are bunchgrass (Agropyron spicatum) and a June grass (Poa sand- 
bergu). Indeed, these areas are often called bunchgrass prairies. 
They constitute the most extensive and valuable lands of the Colum- 
bia Basin, and consist entirely of basaltic soil, except in a few 
gravelly valleys of glacial origin. The upper subdivision is covered 
by a forest of yellow pine. This grows mostly on soils of granitic 
origin above the level of the Columbia lava. 
THE BUNCHGRASS PRAIRIES. 
These constitute a belt of varying width lying between the zone 
of sagebrush below and that of yellow pine above. Altitudinally 
they he between 500 and 800 meters. The bunchgrass prairies are 
best developed in extreme eastern Washington, there constituting the 
rolling hills known as the Palouse and Walla Walla regions. In 
the so-called “ Big Bend Country ” of Lincoln and Douglas counties 
the prairies are very similar, but less rolling. In Yakima and Klicki- 
tat counties the bunchgrass lands are confined to the high plateaus, 
known as the Rattlesnake Mountains and Horse Heaven (PI. XT). 
On the eastern slopes of the Cascade Mountains they are limited in 
extent. 
The basaltic soil of these prairies where the rainfall is compara- 
tively large is a black clay loam, perfectly free from grit. The 
subsoil is similar, but yellowish in color. These soils have originated 
wholly from the decomposition of basalt in place, and vary from a 
few inches to 50 feet or more in depth. Owing to the prevailing 
southwest winds the hills have, as a rule, much steeper north and 
northeast slopes, on which the accumulated soil is unusually fine and 
deep. These moister “north hillsides” support a vegetation much 
like the narrow vales or draws between the hills. 
In regions of decreasingly less rainfall there is a correspondingly 
smaller degree of disintegration of the basaltic rock, which indeed 
often crops out upon the surface. Such rocky lands are locally 
called “scab” or “scablands.” The lie for the most part between 
the typical bunchgrass prairies and the sagebrush plains, but possess 
in the main the flora of the former. 
The bunchgrass prairies (Pl. XIT) are treeless, and excepting along 
streams and by springs, or on north hillsides, shrubs are rarely seen. 
Of the herbaceous vegetation, apart from the grasses, the most con- 
spicuous plants are the lupines (Lupinus ornatus, L. sericeus, and L. 
wyethii), often very abundant; the sunflowers (Balsamorhiza sagit- 
tata and Helianthella douglasii), Gaillardia aristata, Geranium inci- 
sum, and Leptotaenia multifida. In moister places ris missouriensis 
