The Columbia Basin is an arid sagebrush steppe and grassland, surrounded on all sides by areas of higher moisture, predominantly forested, mountainous ecological regions. Habitats within the Blue Mountains ecoregion include desert-like shrubland, grasslands, pine forests and alpine highlands.
A wide variety of habitats and great diversity in native flora exist in the surrounding region. Centered in the dry shrub-steppe region (annual average of 7 in. precipitation) of the lower Columbia Basin, landscapes surrounding the Tri-Cities are dominated by bunchgrasses and sagebrush (Artemisia species). To the east, Walla Walla lies within the rolling hills of the Palouse Prairie or steppe region of Washington where deep loess soils support bunchgrass prairies that grade into shrubs and Ponderosa pine in the foothills leading to the forests and flowers of the Blue Mountains.