176 GEOLOGICAL SURVEY OF THE TERRITOEIES. 



presence may indicate here the upturned edges of the Lower Cretaceous 

 beds. Northward a few miles from the junction of the two Troublesome 

 Creek?, the lava on the east slope of the West Fork seems to draw away 

 from the stream, leaving it apparently on the lignitic beds. A little 

 west of the stream, some exposures dipping westward below the low 

 terraces seem to continue these beds in this direction. (Plate III, sec- 

 tion 3, east end.) Beyond the hills merge gently into the slopes leading 

 up to the great northern lava mass, and are cut by the deep caiion of 

 the North Fork, (not shown in the perspective of the sections.) The 

 extreme western border of the lignitic area, that bordering on the val- 

 ley of the Muddy, will be described when speaking of that valley. 



LOWER TROUBLESOME VALLEY. 



West from the junction of the two forks of the Troublesome, the 

 gentle slopes of two or three low terraces rise to the low divide between 

 the Lower Troublesome and Muddy Elvers. The lower terrace rises 

 about 40 feet above the river-bottom, which is here a few hundred feet 

 wide. Upon the divide the uncompacted, crumbling, light brown and 

 gray sands and white marls of the lake-beds are well exposed, and all 

 the terraces of the adjacent valleys are probably of them. Much alkali 

 here abounds, and the terraces support a thick growth of sage-brush 

 and little if any grass. These beds seem to effectually conceal the 

 structure and relations of the rocks beneath. The divide and adjacent 

 slopes are covered v»'ith boulders, pebbles, and smaller debris of basaltic 

 lava, and moss-agate stones are frequent. Near the divide a few of 

 the higher elevations of white lake-beds are lava-capped, and at one 

 point a mass of lava occurs, as if occupying the ancient channel of a 

 small stream in the lake-beds, (Plate IIIj section 3.) The lava-flow, of 

 which these are the remnants, must have originally extended quite 

 widely over this region, and the greater resistance to erosion due to its 

 presence may have determined the present position of this divide. The 

 latter ends at the south in the rather abrupt and high knob of granite, 

 the Lower Muddy Butte, which will be referred to later. This broad- 

 terraced valley of the Lower Troublesome opens out upon the similar 

 region adjacent to the Grand, and agrees in general features with the 

 lower portions of tbe Williams Eiver Valley, which opens in a similar 

 manner upon the southern side of the Grand. 



VALLEY OE THE LOWER GRAND. 



The region adjacent to the Lower Grand is of terraced lake-beds, 

 through which protrude several small knobs of the metamori)hic rocks. 

 The Grand emerges from its caiion in the red, crumbling, gneisvsic granite, 

 four or five miles below the Hot Springs. At first, the granite forms its 

 northern bank, terraced beds being on the southern side, extending on 

 up the V/illiams Eiver Valley. A little lower, the river cuts somewhat 

 into the latter, leaving a narrow zone of terraces lapping up on the low 

 granite mass at the north. There are here two terraces ; the lower about 

 90 feet high, mostly of soft, dark-gray, friable sands, some compacted, 

 and a few brown conglomerates, a few hundred feet back from which 

 rises the upper terrace, about 125 feet high, capped with a brown con- 

 glomerate of granite debris which forms a small escarpment at the top 

 of the bank. The ravines cutting into the latter open out on to the 

 lower terrace, but do not cut deeply into it. An exceedingly gentle 

 dip of 2'^ or 3° up-stream toward the granite was here observed. The 



