LAKE BEDS OF MOORE CREEK VALLEY. 607 



it is clear that the lake beds are separated from the granite by 

 normal faults. One mile below Warm Springs, on both sides of 

 Moore Creek, there is evidence that the lake beds abut directly 

 against the granite. The same relation is noted at the sandstone 

 bluff, 300 feet high, back of Warm Springs. Here the almost hori- 

 zontal lake beds abut against a steep granite bluff, and a little lateral 

 valley has formed along the contact. There can hardly be any doubt 

 that this steep bluff represents a fault-scarp. The deeply incised 

 gulch just southward gives similar testimony as to the sharp abut- 

 ment of the two formations against each other. 



A small hot spring is located at a point on this fault, and the large 

 warm springs probably also issue from this fault, though at present 

 they break out through the sandstone a little below it. The water 

 has a very high temperature, and the total quantity is probably not 

 less than 100 miner's inches. The water is not rich in dissolved salts, 

 but has a slight smell of sulphureted hydrogen. Mr. J. B. Hastings * 

 thinks that this fault and the accompanying slipping down of this 

 mass of conglomerate or sandstone caused the damming of a lake and 

 the deposition of the lake beds. This can not be accepted as a cor- 

 rect explanation, for the sandstone is of the same age as the lake 

 beds, the deposition of which was caused by events much farther 

 reaching than a landslide. 



All along the southern contact line of lake beds and granite, from 

 Moore Creek below Warm Springs to beyond Bannock Creek, the 

 evidence of a fault is very decided. Nearly everywhere along this 

 line the lake beds cease suddenly, and south of them the granite rises 

 in a steep bluff, contrasting strongly with the confused topography of 

 the soft and sliding lake beds. The best evidence is found at the 

 contact back of Barker's claim, where the contact plane between 

 granite and lake beds is found to dip at an angle of 45 N. A similar 

 and extremely well-exposed fault is shown on both sides of Elk Creek 

 at the northern end of Gold Hill at the mouth of Lincoln Gulch. 



In conclusion, the lake beds of the Payette formation in the Moore 

 Creek basin form an area of about 7 square miles; they dip west or 

 northwest at angles of from 4 to 14, and they are often separated from 

 the granite by marginal faults. They are probably a remnant of a 

 more extensive area preserved by reason of being sunk in the granite 

 by movement along these faults. 



A total thickness of from 300 to 400 feet is exposed above Moore 

 Creek. The idea that rich gold gravel would be found below the lake 

 beds led in 1894 to the sinking of a shaft and bore hole at Idaho City, 

 only about 20 feet above the level of Moore Creek. One hundred feet 

 of shaft were sunk, and then, when the water became too difficult to 

 handle, a bore hole continued down to a total depth of 516 feet. It is 



reported that granitic bed rock was struck at that depth. Samples 



; 



1 Eng. and Min. Jour., July 21, 1894 



