LINDQREN.] TOPOGRAPHY CREEK GRADES. 657 



Creek flows in a similar wide valley with gentle slopes, and passes 

 again lead over to the Pay ette watershed north of Place rville and north 

 of Quartzburg. The lowest pass is the former, which attains an eleva- 

 tion of only 4,700 feet. A short distance west of Granite Creek the 

 Boise Ridge rises very abruptly in the vicinity of Quartzburg, and 

 more gently farther south to elevations ranging up to 7,500 feet. The 

 lowest pass leading across the Boise Ridge, with an elevation of 5,500 

 feet, is found 6 miles west of Centerville. 



One can best appreciate the topographic features of the basin when 

 standing high up on the slopes of the Boise Ridge or on any one of 

 the high peaks rising toward the east. It is seen that the name is 

 extremely appropriate, because it forms a low depression encircled on 

 all sides by a ring of high mountains. Only toward the north, along 

 the water-parting between Boise Ridge and Grimes Pass, is there a 

 lower rim, leading over into the deep canyon of the Payette River. 

 In the accompanying photograph (PL XCI), taken from a point at an 

 elevation of 6,000 feet on the road leading from Quartzburg to Jeru- 

 salem Valley, the encircling rim from Thorn Creek Mountain to "Wil- 

 son Peak is well shown, as are the remarkably level ridges separating 

 the lowest depressions in the basin. 



GRADES OF THE WATER COURSES. 



According to the topographic maps of the United States Geological 

 Survey the grade of the Boise River above and below the mouth of 

 Moore Creek is very slight, being only about 10 feet per mile. 

 Moore Creek for the first 11 miles from its mouth, to the junction 

 with Grimes, has a grade of 40 to 50 feet per mile. The narrow 

 canyon above the mouth of Grimes Creek has a somewhat stronger 

 grade, approximating 66 feet per mile. From Idaho City down to 

 where the canyon begins a grade of 50 feet per mile is obtained; 

 above Idaho City it is for 3 miles 33 feet per mile; beyond this point 

 the grade increases rapidly and is from 100 to 200 feet per mile. 



For the first 9 miles from the junction Grimes Creek averages 40 

 feet per mile; then follow 4 miles of a more abrupt canyon, with a 

 grade of 80 feet per mile. Within the basins of Centerville and 

 Graniteville the creeks have a fall of about 30 feet per mile, which 

 above Pioneerville and Quartzburg rapidly increases to 200 feet per 

 mile. 



TERTIARY AND PLEISTOCENE FORMATIONS. 





 LOWER MOORE CREEK VALLEY. 



Configuration of the valley. From Boise River up to the junction 

 with Grimes Creek, Moore Creek flows in a somewhat broad and 

 U-shaped valley, the slopes of which rise with increasing steepness 

 to ridges with gentle summit lines 2,000 feet above the valley. The 

 hills are covered with a scant vegetation and the soft crumbling 

 18 GEOL, PT 3 42 



