DIKES IN CRANDALL BASIN. 227 



by dikes trending east and west. The bedded breccias continue eastward 

 across the saddle to the first peak of the ridge west of Hurricane Mesa. 

 Near the summit of this peak they are cut off and overlain by beds of 

 breccia dipping slightly toward the east. These beds pass under the massive 

 rocks which form the upper 600 or 700 feet of the western half of this ridge. 

 The massive rocks form nearly horizontal sheets capping the peaks of this 

 part of the ridge and constituting the top of the flat eastern half or mesa. 

 They exhibit prismatic cracking, and appear to be sheets of basalt intruded 

 in the breccia. Beneath them the breccia shows no bedding, and in the 

 eastern part of the ridge — that is, in the mesa — it is highly indurated and 

 weathers like massive crystalline rock with long talus slopes of small 

 fragments. 



On the southern side of the head of Closed Creek the bedded breccias 

 of the Cache Creek divide are cut off near the top of the ridge between 

 Closed and Timber creeks, and are overlain by chaotic slaggy breccia, 

 which exhibits a rude bedding, with steep dip to the eastward. Halfway 

 up the northern slope of the ridge, beneath this point, there is a large 

 irregularly shaped body of massive columnar rock intruded in the breccia, 

 Exposures of massive hornblende-mica-andesite were observed by Mr. Weed 

 on the southern side of the ridge opposite to this body. 



The southern slope of the ridge west of Hurricane Mesa is traversed 

 by dikes running- east and west and more or less parallel. As already 

 remarked, the eastern half of the ridge is a high table-land, whose top, at 

 10,200 feet, consists of a horizontal sheet of basalt, 200 to 300 feet thick. 

 On the south there are steep slopes and spurs, with much slide rock and 

 little vegetation. On the north are four deep amphitheaters, with precipitous 

 walls, and high rocky spurs between them. In the middle of the table-land 

 on the southern side are two narrow gulches encircling a round-topped spur. 



At the western end of this table-land dikes are numerous. Across its 

 southwestern spur there are 11, from 2 to 10 feet wide, trending N. 70° E. 

 and S. 70° E. At the northwestern end of the plateau there are dikes 

 trending northwest, which are well exposed in the wall of the amphitheater. 

 A 10-foot dike follows the ridge along the saddle and cuts the turreted peak 

 to the northwest, The dikes also cut the basalt sheets. The long spur 

 north of this end of the plateau is traversed by 18 narrow dikes trending 

 toward the northwest and converging southeastward toward the round- 



