232 



GUIDEBOOK OF THE WESTERN UNITED STATES. 



part on the east side of that break or fault was forced up many 

 thousand feet, or the part on the west was dropped an equal dis- 

 tance, or both movements took place to a lesser degree. It matters 

 not which side moAed, for in any event the part east of the fault now 

 forms mountains because it was uplifted relative to the other, or the 

 other is now a low basin because it was depressed relative to the part 

 on the east.®^ Althojiigh the principal movement probably took place 

 long ago. slight movements have occurred so recently that they have 

 broken across alluvial cones formed by small streams flowing out 

 of the mountains. 



A short distance beyond Mapleton the railroad cu*rves to the right 

 and approaches the edge of the plain. There it begins to descend to a 

 lower plain, which stretches away in the distance as 

 far as the eye can see. Before reaching the level of 

 the lower plain the railroad passes through the 

 flourishing town of Springville (see sheet 10, p. 244), 

 which is surrounded not only by fields of grain, 

 alfalfa, and sugar beets but by orchards that stretch out mfle after 

 mile until they seem to be interminable. It is indeed a land of peace 

 a«id plenty, and an added beauty is given to the scene by the still 

 waters of Utah Lake shimmering in the bright sunshine. A branch 



Springville. 



Elevation 4.555 feet. 

 Population 3.010. 

 Denver 696 miles. 



^ The entire Great Basin, which ex- 

 tends from tlfe Wasatch Range on the 

 east to the Sierra Nevada on the west, 

 is characterized by faulted mountains 

 like the Wasatch. Such mountains 

 are generally known as " block moun- 

 tains," for the reason that the crust 

 of the earth has been broken into great 

 blocks by the faults and later these 

 blocks have been tilted in different 

 directions. In the central part of the 

 basin the faults and consequently the 

 block mountains trend north and 

 south, as may be seen on any good 

 map of the region. The beds of rock 

 of which such a mountain is com- 

 posed may originally have had a sim- 

 ple structure or they may have been 

 folded and broken in a most complex 

 manner. But no matter how complex 

 the folding the block has acted as a 

 unit and has been tilted in the same 

 manner as the horizontal rocks. 



In the tilting the edge of the great 

 block that was elevated produced a 

 mountain and the edge that was de- 

 pressed formed a deep basin, which 



later was partly filled by sand and 

 gravel washed in from the surround- 

 ing slopes. In many places the loose 

 rock filling has a depth of more than 

 a thousand feet. Such a basin is gen- 

 erally deepest in the center, and the 

 slight precipitation that falls on the 

 surrounding slopes finds its way to the 

 lowest point, where it forms a shal- 

 low lake, but the water is soon car- 

 ried off by evaporation and there re- 

 mains in its place only a dry lake bed, 

 known in the Southwest by the Span- 

 ish name of " playa." The entire 

 basin is also frequently spoken of as 

 a "boLson" (bowl-sown'), a Spanish 

 name meaning purse, which has been 

 applied to the basin because it re- 

 sembles in shape a Spanish purse. 



Great Salt Lake is said to lie in 

 .such a basin, though it really lies in 

 .several basins, which are so shallow 

 that the water extends from one to the 

 other. In time of drought it too 

 would disappear were it not for the 

 large supply of water it receives from 

 the high ranges on the east. 



