226 GEOLOGY OF THE YELLOWSTONE NATIONAL PARK. 



being 1 situated at the east Besides these dikes others were observed at the 

 eastern end of the ridge, and 6 or 7 were found by Mr. Weed at the western 

 end, making over 40 in all. 



From the distribution and trend of these dikes it is evident that they 

 radiate from that portion of Hurricane Mesa which is situated between the 

 deep gulches just alluded to. The dikes are not absolutely straight, but 

 trend in general toward this spot. They are more numerous directly south 

 of it, where the ridge is nearest to this center, and are less frequent toward 

 the west, where the ridge is more remote. 



The southern slope of the ridge north of Timber Creek is traversed 

 by dikes of the same kinds of rocks as those occurring on the crest, and 

 having similar trends, leaving no doubt that they are continuations of the 

 same dikes. The breccia cut by these dikes is indurated where they are 

 close together. It is to be remarked that all parts of the country in this 

 vicinity which were explored were found to be traversed by dikes, but, 

 owing to the limited amount of time and the difficulty of traveling, a thor- 

 ough exploration of the country was not made, and only those dikes which 

 were observed, sometimes from a distance, have been mapped, their probable 

 continuations being indicated by dotted lines. 



On the end of the northeastern spur of Indian Peak there are dikes, 

 some of which trend west of north toward the center on Hurricane Mesa, 

 while others trend northeast. Dikes trending northeast occur on the ridge 

 between Papoose and Hoodoo branches of Crandall Creek. 



The structure of Hurricane Mesa and the ridge west is clearly seen 

 from the ridge south of it. A sketch of it was made from a point on the 

 northeast spur of Indian Peak (PL XXXI). It shows the ridge with its 

 eastern table-land, from 10,000 to 10,600 feel in altitude, and the western 

 chain of peaks, reaching heights of from 10,400 to 10,800 feet; the valley of 

 Closed Creek, whose bottom has been eroded down to 8,000 and 6,800 feet; 

 the steep narrow ridge south of the latter, whose high point in the middle 

 ground is 9,600 feet, and the valley of Timber Creek, with the divide to 

 Cache Creek, at about 9,500 feet. To the right is the outline of Hunter 

 Peak, at the mouth of Crandall Creek. 



The western head of the valley of Closed Creek, which is the divide 

 to Cache Creek, consists of horizontally bedded breccia with a slight dip 

 to the southwest. It contains a few intercalated flows of basalt and is cut 



