96 



GUIDEBOOK OF THE WESTERIN' UlNITED STATES. 



to the level of the Provo terrace, which was built by this lake when 

 its surface remained for a long time at an elevation about 625 feet 

 higher than the present lake. 



by the resulting increase of evaporation 

 surface, and the effect of a series of dry 

 years h lessened by the resulting reduc- 

 tion of surface exposed to evaporation. 

 This natural and automatic control lim- 

 its the range of oscillation and gives a 

 certain permanence to 'what may be called 

 a normal or avera^^re level. A change in 



normal 



introduced 



Both man and nature have introduced 

 new factors and thus have produced 

 changes in the normal level. Tlie occu- 

 pation of the surrounding region by white 

 men has recently modified the face of 

 the land in ways that have a recognized 

 influence on the water level; and the 

 ancient history of the lake includes 

 enormous modifications in response to 

 changes of climate. 



Of human influences the most telling _ _ „, 



has arisen from^the development of agri- | supply and loss of water ma^yalsobe'dL" 



culty can the bather keep his feet from 

 rising to the surface, and if he balances 

 himself in an upright position his head 

 and shoulders are above the surface. 



The brine is weakest in the northeastern 

 arm, the portion visible from the train 

 near Brigham. This arm has been par- 

 titioned from the main body by the em- 

 bankment of the Southern Pacific Co. 

 and is continuously supplied with fresh 

 water by Bear River. Ice can form on 

 the stronger brine only in zero weather, 

 but this arm is frozen from side to side 



every winter and sleighs have been driven 

 across it. 



The only climatic element with which 

 the lake oscillations have been connected 

 by direct obser^-ation is precipitation 

 the lake rises or sinks as the fall of rain 

 and snow is great or small — but it is easy 

 to understand that the balance between 



culture with irrigation. In irrigation the 

 water of rivers and creeks is diverted to 

 cultivated fields, which first absorb it 

 and then through evaporation feed it to 

 the air; and the water thus constuned 

 by utilization is lost to tlie lake. "With 

 the gradual enlargement of the irrigated 



level of the lake is 



normal 



inevitably being lowered, and engineers 

 are already confident that the high-water 

 mark of 1877 will never again be reached. 

 On the other hand, there is no reason to 

 expect the lake's extinction, for there ia 

 a limit to the possibilities of irrigation. 



The fresh water brought by the rivers { 

 mingles gradually vdth the brine, and as 

 the river mouths are on or near the eastern 

 shore, the brine is not so strong at the east 

 as at the west. Analyses from samples of 

 the brine gathered at different points and 

 in different years report the dissolved 

 solids as from 13.7 to 27.7 per cent, by 



turbed by any change of climate which 

 affects the rate of evaporation. As every 

 laundress well knows, evaporation is 

 favored by heat, by dryness of the air, and 

 by strength of wind and is retarded by 

 cold, by moisture in the air, and by calm. 

 So there are at least four ways in which 

 changes of climate may cause the lake to 

 xpand or contract. The latest of the 

 periods into which geologists divide past 

 time witnessed a series of climatic changes 

 which affected the whole earth, and 

 though all the elements just mentioned 

 were doubtless involved, the element 

 which recorded its changes most clearly 

 waa temperature. There 



weight. A 

 contained 1 



time 



August 



At the 



imes that 



than that 



'nsity 



iffi 



several 



epochs of cold, and they were separated 

 by epochs of warmth. During the cold 

 epochs the high parts of the Wasatch 

 Eange held a system of glaciers, and in 

 one of them several icQ tongues protruded 

 so far beyond the mouths of the mountain 

 canyons that they heaped their moraines 

 on the floor of Jordan Valley, only a few 

 miles from the place where Salt Lake 

 City now stands. In that epoch of cold 

 the rate of evaporation was far slower than 



now. and f;vannratinTi was nt .so ereat a dlS" 



