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GUIDEBOOK OF THE WESTERN UNITED STATES. 



dotted with farms, each protected by a line of tall poplars that may 

 be seen far across the valley. Utah Lake, a body of fresh water 30 

 miles long and 6 to 10 miles wide, lies in the middle of the basin. 



lower levels they left behind the shapes 

 their waves had made. The base of 

 each surviving shore cliff is a hori- 

 zontal line, and so is the crest of each 

 beach, bar, and spit, and these features 

 in combination trace the outline of the 

 old lake as a level contour about the 

 sides of the basin and the faces of 

 mountains that were once islands in 

 the lake. 



■' In rising and falling the waters 

 lingered at many levels, and so there 

 are many ancient shore lines, but two 

 of them are more conspicuous than the 

 rest and have been named. The high- 

 est of all is the Bonneville shore line, 

 and 375 feet lower lies the Provo shore 

 line. The Bonneville line represents a 

 relatively short stand of the water and 

 is conspicuous chiefly because it marks 

 the upper boundary of wave action. 

 All the slopes below it have been more 

 or less modified by the waves, but 

 the slopes above it retain the shapes 

 which had been given them by other 

 agencies. The Provo line represents a 

 long stand of the water and is conspic- 

 uous because it is strongly sculptured. 



•' In all the early history of the great 

 lake its basin was closed, like that of 

 the modern lake. The water surface 

 rose and fell in response to climatic 

 changes like that of its modern rem- 

 nant. The last great rising was the 

 highest and terminated the series of 

 oscillations by creating an outlet. The 

 lowest point of the basin's rim was at 

 Red Rock Pass [130 miles by rail 

 north of Salt Lake City], and when 

 the water rose above that level the 

 stream which began to cross the pass 

 descended to Portneuf River, a tribu- 

 tary of Snake River, the chief branch 

 of the Columbia. Through the creation 

 of this outlet the Bonneville Basin, 

 which had previously contained an in- 

 dependent interior drainage system, be- 

 came part of the drainage system of 

 the Pacific Ocean. * * * 



" The formation at the summit [of 

 Red Rock Pass] consisted of soft 

 earth, and as soon as overflow began a 

 channel was formed. The deepening 

 of the channel increased the volume of 

 the stream by lowering the outlet of 

 the lake ; the greater stream was more 

 efficient in deepening the channel, and 

 these two causes interacted until the 

 stream became a stupendous torrent. 

 The volume of water discharged before 

 the flow became steady was enough to 

 supply Niagara River for 2.5 years, but 

 the record of the torrent's violence 

 leads to the belief that it lasted for a 

 much shorter period. * * * 



" The draining of the lake down to 

 the Provo level reduced its area by 

 one-third and correspondingly reduced 

 the quantity of water annually evapo- 

 rated. Two-thirds of the inflowing 

 water was then disposed of by evapo- 

 ration, and the remainder was dis- 

 charged through the outlet. Only a 

 great change of climate could restore 

 the balance between inflow and evapo- 

 ration, and the change was slow in 

 completion. At last, however, the pen- 

 dulum of temperature swung far 

 enough on the side of warmth. The 

 outlet channel ran dry, the lake basin 

 was again separated from the drain- 

 age system of the Pacific, and the lake 

 began to shrink. So long as there was 

 outflow the water was fresh, but when 

 the outflow ceased there began that 

 accumulation of salt which has made 

 the water of the present lake a concen- 

 trated brine. 



"At times in the history of the lake, 

 especially while the Provo shore line 

 was being formed, the tributary 

 streams brought down sand and 

 gravel, which they dropped at their 

 mouths, building deltas. When the 

 water fell these deposits remained as 

 fan-shaped benches having steep 

 fronts. The streams that built them 

 then dug channels through them. * * * 



