48 CONTRIBUTIONS FROM THE NATIONAL HERBARIUM. 



sions. The lower subdivision is grass-covered and lies immediately 

 above the zone of the sagebrush. The consi)icuously abundant plants 

 are bunchgrass {Ayropyroti spicatinri) and a June grass {Poa smul- 

 hergii). 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 abov-e the level of the Columbia lava. 



,_ THE BUNCHGRASS PRAIRIES. 



These constitute a belt of varying w idth lying between tlio zone 

 of sagebrush below and that of yellow pine above. Altitudiiially 

 they lie 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, 

 knowm as the Rattlesnake Mountains and Horse Heaven (PI. XI). 

 On the eastern slopes of the Cascade Mountains they are limited in 

 extent. 



The basaltic soil of these prairies wdiere 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 (PI. XII) 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 Ilelianthella douglasii), Gaillardia aristata^ Geranium inci- 

 sum, and Leptotaenia midtiflda. In moister places Iris missourienai^ 



