IJNDGEEN.] GRAVEL AND BASALT OF THE BOISE RIDGE. 675 



reaches high up on the ridge between Fall and Granite creeks nearly 

 to the Newburg or Lawyer quartz claim. It is said to be quite rich 

 here, though hard, and difficult to work on that account and because 

 of the scarcity of water. On this ridge the older gravel distinctly 

 rests on the granite, and its thickness reaches a maximum of 200 feet. 

 Its highest elevation on the ridge near this quartz mine is 4,900 feet, 

 or 500 feet above the upper end of Kennedy's claim. 



Gravel on the Boise Ridge. A very remarkable occurrence of 

 gravel was found on the summit of Boise Ridge 3 miles west-north- 

 west of Quartzburg. The broad, flat summit extends northward from 

 Hawkins Pass, with a winding direction, caused by the deeply incised 

 gulches, and an elevation of from 6,500 to 7,300 feet above the sea. 

 North-northwest of Quartzburg lie, on the summit, several hundred 

 feet of scoriaceous basaltic flows, which extend down into Jerusalem 

 Valley on the west. In this basalt there occurs, at an elevation of 

 6,900 feet, one-half mile south of the sharp point, with an elevation 

 of 7,200 feet, a small body of gravel. It could not be determined 

 whether this gravel is intercalated between the basalt beds or forms 

 an inclusion in the same, but the former is more probable. At any 

 rate, the gravel is well washed, of granitic character, and is said to 

 contain some gold. This occurrence is of the greatest interest, as it 

 clearly indicates that a very great disturbance has taken place since 

 the eruption of these basalts, for the gravel could not possibly have 

 been formed with the present topographic features. Considered in 

 connection with the faulted old gravels at the eastern foot of the 

 escarpment, 2,700 feet lower, it points to a great disturbance along 

 the eastern base of the Boise Ridge. 



Basalt. The whole of the high portion of the Boise Ridge south of 

 the latitude of Quartzburg is remarkably free from any late erup- 

 tions. At the locality mentioned in the preceding paragraph, culmi- 

 nating in the hill with an elevation of 7,200 feet north-northwest of 

 Quartzburg, the very even, flat surface of the granitic ridge is capped 

 by 300 feet of massive basalt. Above the massive basalt lie 200 feet 

 of tuff and scoriaceous basalt, again covered by 100 feet of fresh and 

 massive olivine-basalt. These basaltic flows slope rapidly westward, 

 and the ridge on the north side of Brainard Creek is, as seen in PI. 

 LXXXIX, composed of a great number of superimposed thin basaltic 

 flows, all dipping northwest at angles of 30 or 35. The photograph is 

 taken from a gap in the ridge between Brainard and Porter creeks, 3 

 miles west-southwest from the high basalt peak in the Boise Ridge. 

 Taken in connection with the probable fault along the eastern side of 

 the range at Granite, it certainly appears as if a westward tilting had 

 formed part of the orographic movements in this vicinity since the 

 time of the deposition of the lake beds. The basalt is much older 

 than the basalt of the lower Moore Creek, and in all probability is 

 contemporaneous with the lake beds. 



