The Blue Mountains of southeastern Washington differ from other ranges in Washington in their relative aridity. There are few streams and a single river drains the area. There are no government weather stations in the Blue Mountains. The winter temperatures are low and the snow deep and lasting. Summer temperatures are high and humidity and precipitation low. Coniferous forests of the type of arid regions form the principal tree cover. Typical plant species include the white fir (_Abies grandis_), alpine fir (_Abies lasiocarpa_), larch (_Larix occidentalis_), spruce (_Picea columbiana_), and such shrubs as fool huckleberry (_Menziesia ferruginea_), _Pachystima myrsinites_, dogwood (_Cornus canadensis_), wild current (_Ribes petiolare_), mountain mahogany (_Cercocarpus ledifolius_), spirea (_Spiraea_ sp.), lupines (_Lupinus_) of several species, maple (_Acer douglasii_), buckbrush (_Ceanothus sanguineus_), sticky brush (_Ceanothus velutinus_), and huckleberry (_Vaccinium membranaceum_). [Illustration: FIG. 10. A "pothole" being crowded by drifting sand, ten miles south of Moses Lake, Washington, March 23, 1940. (Fish and Wildlife Service photo by Victor B. Scheffer, No. 925.)] The Columbian Plateau and southeastern Washington present desert conditions. At Odessa, 1590 feet, Lincoln County, the average annual precipitation is only 9.38 inches, and only in the winter may more than one inch of precipitation per month be expected. The average temperature is 48.5°. In the winter the average is below freezing but in July it is 71.3°. The average maximum for July is 90° and an extreme of 111° is recorded. Walla Walla, 991 feet, has a higher annual precipitation (16.66 inches) but higher temperature (yearly average 53.5°, July average 75.0°, average July maximum 88.6°, extreme 113°). Winter temperatures on the Columbian Plateau are low. The January average at Odessa is 25.3° and at Walla Walla 32.4° The average yearly snowfall at Odessa is 19.4 inches and at Walla Walla 23.5 inches. Vegetation of the Columbian Plateau and southeastern Washington is of the desert type. A few pines and junipers grow in favored places. Along streams the cottonwood (_Populus hastata_) and willow (_Salix_) of several species are common. Most typical are grasses and shrubs such as the bunch grass (_Agropyron inerme_, _Agropyron spictatum_), foxtail (_Alopecurus aequalis_), cheat grass (_Bromus tectorum_), saltbrush (_Atriplex truncata_), greasewood (_Sarcobatus vermiculatus_) mustard (_Arabis_ sp., _Brassica_ sp.), sagebrush (_Artemisia rigida_, _Artemisia tridentata_), rabbit brush (_Chrysothamnus nauseosus_, _Chrysothamnus viscidiflorus_) and cactus (_Opuntia polyacantha_). The arid climate of the Columbian Plateau affects, to some extent, surrounding areas. Thus the Yakima Valley Area, the Columbia Valley, where it borders the Plateau, and the Okanogan Valley possess vegetation typical of the Columbia Plateau. LIFE-ZONES AND ECOLOGY