128 SCIENCE AND SOIL 



purposes. They are used chiefly for grazing and, to some extent, in the pro- 

 duction of hay, grains, and in some sections for vegetables. 



Yakima series. Ash-gray to light brown soils derived principally from 

 ancient lake sediments consisting of an admixture of volcanic dust and ba- 

 saltic, andesitic, and granitic materials. Certain members of this series have 

 been very successfully developed for hop culture, alfalfa, grass, grain, and 

 fruit, while other members of the series, owing to their elevated position and 

 general rough character, have not been developed at all. 



ROCKY MOUNTAIN VALLEYS, PLATEAUS, AND PLAINS 



The soils of the Rocky Mountain valleys, plateaus, and plains are derived 

 from a wide range of igneous, eruptive, metamorphic, and sedimentary rocks. 

 The plateau and plain types occupy a more or less elevated position, and have 

 sloping, undulating, or irregular surface features. They are derived from 

 underlying sedimentary rocks or consist of the remains of the ancient extensive 

 mountain foot-slope material or of alluvial deposits along streams trenching and 

 terracing the sedimentary rocks of the plateaus and plains. The mountain slope 

 and intermountain types consist of residual and colluvial deposits or of ancient 

 lacustrine or later stream sediments, occupying mountain foot slopes and 

 narrow valleys. 



The soils of the mountain slopes are usually of little agricultural value, 

 owing to their rough surface, elevated position, and the consequent imprac- 

 ticability of irrigation. Those of the plateaus, valleys, and plains vary widely 

 in economic importance, depending largely upon climatic features, topography, 

 position, and water supply for irrigation. They range from grazing lands 

 of nominal value to soils adapted to the most important and intensively culti- 

 vated fruit, melon, sugar beet, and other special crops. 



Billings series. Compact adobe-like gray to dark or brown soils and sub- 

 soils, formed mainly by reworking of sandstones and shales, and occupying old 

 elevated stream terraces. This is an important series adapted to alfalfa and 

 general farm crops and stock raising ; also used to a considerable extent in the 

 production of sugar beets. 



Colorado series. Light gray to reddish brown soils and subsoils, derived 

 from colluvial wash. Where irrigable, these soils are important soils in the 

 production of alfalfa, sugar beets, melons, and, to a limited extent, fruits. A 

 number of the soils of the series, however, are so situated as not to be suscep- 

 tible to irrigation, and have not been developed for agricultural purposes. 



Finney series. Brown to nearly black soils derived from glacial material 

 underlain by lighter-colored subsoils. The heavier soils may be dry farmed 

 to advantage, and would become very productive with irrigation. The lighter 

 soils have a broken surface, are porous, and easily drifted by the wind. They 

 are best adapted to grazing. 



Fruita series. Reddish brown soils, formed by reworking of sandstones 

 and shales, occurring as stream terraces. When well drained and free from 



