854 C. R. KKYEIS UUOGJiAl'mC OHUa^' OK LAKK IJONNKVILLK 



linJI:' of the lotal inflow, lias an uiiiisua] course. It first flows nearly 

 north, then turns sharply back on itself and runs almost due south. On 

 leaving the mountains its canyon immediately opens out into a broad 

 transverse intermont plain known as Cache Valley, which was at the 

 time of its greatest expansion a long arm of the lake. On either side of 

 the canyon's mouth the highest lake terraces are well displayed. Cache 

 V^alley also leads into the Eed Eock Pass, which Gilbert is confident was 

 once occupied by the lake's outlet to the Snake River of Idaho. The two 

 locations are thus only a few miles apart. Accordingly, the inflow and 

 outflow take place at practically the same point. Both are at the lowest 

 spot in the lake's rim. Under such conditions the formation of any lake 

 would be almost an impossibility except through means of especial pre- 

 lacustrine circumstances, of which there has been as yet no suggestion. 



PRECLUSION OF REGIONAL OSCILLATORY CHANGES 



It is passing strange that in the very birthplace of that most brilliant 

 of geologic concepts — the fault-block hypothesis of Basin Range structure, 

 whereby the mountain prisms are fancied as tilting and floating as do 

 ice-cakes in a river at time of spring break-up^ — the probability and even 

 possibility of orogenic movement should be so com]detely overlooked 

 when the chief Bonneville Lake problems came up for consideration and 

 solution. There are in the region abundant evidences of recent dias- 

 trophic oscillations. Some of these disturbances were manifestly very 

 considerable and took place in quite late geologic times. The lake ter- 

 races themselves plainly show notable warping. On the west side of the 

 (Ireat ])asin the Inyo earthquake, which occurred within the memory of 

 men yet living, was accompanied by displacements of over 30 feet. A 

 warping of less than 200 feet would direct the present headwaters of 

 Snake River from the Bonneville basin, if they ever formed a part of that 

 drainage system. On the other hand, an uprising of 1,000 or 1,200 feet 

 at the south would effectually bar the waters of the lake at the time of 

 its greatest expansion from reaching the Colorado River. The actual 

 uprising of this tract, as indicated by the depth of the inner gorge of the 

 Grand Canyon in this vicinity, is more than twice this figure. Such 

 facts go to show in no unmistakable way that no consideration of the 

 origin of Lake Bonneville is complete without ci'itical determination of 

 the values of the diastrophic factors. 



INATTENTION TO PRE-LACUSTRINE CONDITIONS 



The history of Lake Bonneville really does not begin with the lake as 

 such at all. It goes back far beyond the time when the empounded 



