YAHOO CANYON. 139 



Lake and is the only one ot" tlic principal (lraina<;ti channels ot" tlii' Mahogany 

 Hills that follows a north and south course. At one time it drained the 

 depressed basin of Dry Lake. At the head of Yahoo Canyon a small out- 

 burst of rhyolite forms a low obscure hill, around which the wagon road 

 passes on the west side. A few hundred feet to the south of the hill is a 

 dike of similar rock about lOO feet long by 2.") feet wide. This rhyolite 

 is a light gray rock, weathering brown, and carrying a few macroscopic 

 secretions of biotite, sanadin, and quartz; it closely resembles the rhyolite 

 of Browns Canyon. Yahoo Canyon presents some interest as being the 

 dividing line between two quite different types of orographic structure; on 

 the west side the plateau-like body of limestones in the neighboi-hood of 

 Devon and Temple Peaks lies gently inclined to the westward, while on the 

 east side the limestones have been uplifted into longitudinal ridges with the 

 structural peculiarities of the Pinon Range. In general the canyon may be 

 said to have been eroded along the axis of an anticlinal fold, although this 

 is not strictly correct, as on the east side near its lower end a sharp anti- 

 clinal ridge exists, which, however, dies out toward the head of the cauA-on. 

 The structural details are i-ather intricate and were b}^ no means carefully 

 workeil out, but the dips and .strikes indicated on the map (atlas sheet v.) 

 show this anticlinal structure with the trend of the ridges agreeing with the 

 coui-se of the canyon. The main ridge of limestones east of Yahoo Canyon 

 inclines invariably to the eastward with an average dip of about 35° and 

 with a strike a little west of north, maintaining this position till passing 

 beneath the Carboniferous rocks which everywhere seem to overlie them 

 confonnably. The ridge is made up of monotonous blue massive lime- 

 stcmes characteristic of the Upper Nevada epoch as seen elsewhere, espe- 

 cially in the neighliorhood of Signal T*eak on the west side and Newark 

 iMountain on the east side of the district. ( )n the east side of Yahoo 

 Canyon a most interesting collection of characteristic species was made, 

 consisting largely of Upper Devonian corals. Associated with them occurs 

 such distinctive species as Spirifera disjuncta and the widely distributed 

 Spirifim (/labra ; a fauna indicating a higher horizon than any of the ex- 

 amined beds in the Mahogany Hills to the west. A list of the fauna 

 obtained is given on page 83. Between this locality and the Diamond 



