666 IDAHO MINING DISTRICTS. 



lake beds are not exposed, but the gravel of the terraces is reported 

 to rest on them. Across Elk Creek from Gold Hill sandy and clayey 

 lake beds again appear, the bench gravels resting on their eroded 

 surface. Granite appears a short distance up on the hillside. 



Around East Hill and Gold Hill the lake beds are well exposed, and 

 consist largely of greenish or gray clay with arenaceous streaks and 

 intercalated beds of black clay with coaly streaks. The dip is 10 W. 

 A few fossil plants were found here, which were identified by Mr. 

 Knowlton. (See Appendix, p. 721.) 



These plants identify the lake beds with the Payette formation of 

 the foothills, a correlation which the field work had shown to be very 

 probable. Considerable masses of fossil wood are reported to have 

 been found in the lake beds at the mouth of Steamboat Gulch, 1 mile 

 southeast of Idaho City. 



The lake beds attain their greatest development south of Idaho City, 

 where they are more than 300 feet thick. Their character is here 

 prevailingly sandy, with some medium-coarse gravels and with occa- 

 sional coaly and clayey layers. The exposure illustrated in fig. 58 



FJO. 59. Bench gravel and lake beds at mouth of Granite Creek, 2 miles west of Idaho City. 



indicates an apparent unconformity in the lake beds. They continue 

 up the creek, decreasing in width, to the mouth of Granite Creek. 

 Good exposures are seen at Brockhausen and Spiro's claim, between 

 Granite and Bannock creeks, where the bench gravels rest on them. 

 Fine gravels here appear in the lake beds, interstratified with clay and 

 sand. At the little bench just south of the mouth of Granite Creek, 

 12 feet of lake beds, dipping 4 W., at first gravelly, then sandy, rest 

 on granite, and on the eroded surface of the lake beds rests a patch 

 of bench gravel 50 feet above the main creek. A few quartz pebbles 

 are present in the gravel of the lake beds (fig. 59). 



A small area of clayey lake beds is said to exist on the high plateau 

 several hundred feet above Moore Creek and about 2 miles east- 

 southeast of the mouth of Granite Creek. 



The contacts of the lake beds with the granite offer points of great 

 interest. It has already been noted that lake beds rest on granite 

 near Turner's claim, at the east end of Gold Hill, and at the mouth of 

 Granite Creek. Everything indicates that they were laid down on an 

 uneven surface, and probably in a valley with configuration similar 

 to that of the present Moore Creek Basin. But at many other places 



