10 NOBTH AMERICAN FAUNA [No. 55 



interest in these ancient bodies of water lies mainly in the rich 

 fossil beds that here and there mark the old shore lines. Some of 

 the " badland " formations of these old beaches bear valuable de- 

 posits of prehistoric mammal remains that open an important chap- 

 ter in the geological history of the State. The John Day Valley, 

 Camp Creek, Malheur, and Owyhee Valley fossil beds are probably 

 the best known. 



GLACIATION 



Glaciation as a type of drainage has modified to some extent the 

 higher elevations of the State and is still slowly eating away great 

 cirques and amphitheatres on the upper slopes of Hood, Jefferson, 

 the Three Sisters, McLoughlin (Pitt), the Wallowa, Baker, and 

 Steens Mountains. Ancient moraines show glacial activity much 

 lower on the mountain slopes than at present. Generally this evi- 

 dence does not extend into the valley country, nor is it conspicuous 

 after the great volcanic period. Glacial lakes are comparatively few 

 in the State, although Wallowa Lake is a beautiful example of a 

 glacial scoop and some of the smaller lakes high up in the moun- 

 tains owe their origin to the ice. Many, if not most, of the lakes 

 in Oregon, however, owe their origin directly or indirectly to vol- 

 canic activity closing up valleys or damming streams of water with 

 streams of lava. 



SOIL CONDITIONS 



Soils and land coyer, in special cases, exert considerable influ- 

 ence on the distribution of species. Over much of Oregon the firm, 

 rich, dark-colored soils from disintegrated lavas are generally fer- 

 tile and produce dense plant growth. They vary endlessly, however, 

 in texture, in mineral composition, and in mechanical structure. 

 At one extreme are the fine precipitates of deep-water deposits, form- 

 ing tenacious clays, commonly called " gumbo." Waxy when wet 

 and hard when dry, they are extremely discouraging to most bur- 

 rowing rodents. At the opposite are the deep mellow sands, fine 

 and nonadhesive, that form light mellow soils. These always prove 

 a great delight to burrowers. 



Only very limited areas of the light, water-washed sands, such 

 as drift and change with every wind, are found, mainly along the 

 Columbia River Valley above The Dalles, around the shores of 

 Harney and Alvord Lakes, and in places along the coast. In these 

 spots the light yellow sands drift back over the river banks, lakes, 

 and seashore in dunes and ridges for considerable distances, giving 

 their color and character to extensive areas. While attracting or 

 developing certain species of plants and animals, these light sands 

 have perhaps crowded out others with different affinities. Sand 

 dunes in the desert are favorite haunts of kangaroo rats, pocket 

 mice, lizards, and horned toads. Another soil type favorable to 

 burrowing species of mammals, as well as horned toads and lizards, 

 is composed of the deep, black, loose sands and volcanic ash, espe- 

 cially conspicuous east and south of the Paulina Mountains. This 

 soil is attractive also to sand- and heat-loving plants. 



Owing mainly to soil conditions, the extensive playas of the Alvord 

 Valley and others east of the Steens Mountains, except for brief peri- 



