OEEGOTT SHOKT LIXE OGDEX TO YELLOWSTOXE. 



125 



r 

 * 



At Tyhee (see sheet 15Cj p. 138), IJ miles south of the Fort Hall 



Reservation 



Tyhee. 



Elevation 4,45S feet, 

 Ogden 140 miles. 



is obtained on the left of the middle and east huttes 

 of the three already mentioned. The sagebrush flat 

 now being crossed is owned by the Indians, Very 

 little land has been cultivated in this part of the reser- 

 gh much of the land is under ditches of the irrigation 

 [ed by the Government. Near Tyhee may be seen the 

 large upper canal which takes water from Blackfoot River about 15 



em 



directly underlain by sheets of basalt. 

 Tlie last of the extensive volcanic dis- 

 charges happened in very recent times, 

 and the process of Btream deposition still 



continues. 



The estimated area covered by the 

 Snake River lava is in the neighborhood 

 of 20.000 square miles. So far as is now 

 definitely known, there is but one la^-a 

 field in North America of greater extent, 

 namely, the Columbia River lava, the 

 estimated area of which is about 200,000 

 square miles. In Snake River canyon, 

 below Shoshone Falls, nearly 700 feet of 

 lava in horizontal sheets are exposed, 

 but whether this is the maximum thick- 

 ness or not can not be told. As a rule, 



are 



Valley. Like each of these formations, it 

 is of exceptional fertility if properly 

 irrifrated . 



The ever-present and characteristic 

 plant of the Snake River plains is the 

 sa^^ebrush (Artemisia tridenlata), which 

 grows abundantly and, we might say, 

 luxuriantly in the dr^^ soil from the bot- 

 tom of the Snake River canyon up to an 

 elevation of some 2,000 or 3,000 or more 

 feet on tlie mouutaiua bordering the 

 plains. It covers the broad arid valleys 

 almost completely and is seldom lacking 

 over any extensive area except where 

 fires have rocentlv occurred or cultivated 



pplant 



On the plains in sum- 



perhap 



widely extended. That many inde- 



^pendent outflows of lava have occurred 



is easily seen, but in the walls of Snake 



River canyon, where the best sections 



■nu 



the number unless lacustral deposits, 

 beds of lapilli, etc., occur between them. 

 Although the soil of the Snake River 

 plains has well-marked variations, it may 

 be said that in general, and, in fact, almost 

 everj^where, it is fertile and needs but 

 .the requisite moisture to enable it to pro- 

 duce a strong growth of either native or 

 cultivated plants. In general, however, | that they are practically without water, 

 the soil of the plains is a fine yellowish- Comparatively little of the surface is des- 

 white siltlike material, largely a dust de- titute of plant life. In fact, the flora is 

 posit, which mantles the surface not only 



mer fire sometimes sweeps through the 

 sagebrush in much the same manner that 

 it does over the prairies and ''burns'' are 

 produced. The *'sage" in the localities 

 most favorable to its growth attains a 

 height of about 10 feet, but usually is not 

 over 3 feet high, the clump of bushes 

 being commonly 6 to 8 feet apart. One 

 can ride or walk over the sagebrush plains 

 with but little difficulty. The light 

 gra>-ish-green leaves of this ubiquitous 

 plant give color, or perhaps more prop- 

 erly, lack of color, to the plains and en- 

 hance their monotony. Although the 

 Snake River plains are frequently termed 

 a desert, the name is true only in the sense 



tracts, but covers hills and 



simi 



depressions alike. This material i^ 

 lar to the celebrated loess of China, except 

 that it usually occurs as a comparatively 

 tliin layer, and resembles also the deposit 

 bearing the same name in the Mississippi 



aried 



examines 



are man 



blossom 



spring, filling the air with fragrance, and 

 in the summer and fall the yellow of 

 sunflowers and of the still more plenti- 

 ful *^ rabbit brush" (Bigelovm graveohns). 



