90 GEOLOGY OF THE DEFVEK BASIN. 



or slightly overthrown, remain so, and the Triassic beds alone have an 

 inclination under 80 or 90 . North of this, whore regularity in the forma- 

 tions once more prevails, the dips settle hack approximately to their 

 normal amounts as given at Bear Creek. 



The general fold parallel with the base of the Colorado Range Tile Surface eXpOSIUVS 



of the prominent and sharply denned fold occurring generally along the 

 base of the Colorado Range and resulting from its uplift are, for the 

 greater pari of the area under consideration, to be found within a short 

 distance of the line of union of the Denver and Arapahoe formations. 

 North of Van Bibber ('reek, however — where the Denver formation 

 ceases to exist, and where, "_' or ,"> miles farther, the Arapahoe also 

 disappears— the Wend is almost entirely transferred to the Laramie, the 

 Arapahoe lor that part of the distance over which it is present entering 

 into it only in the slightest degree. 



Faults. — There are along the line of the older formations in this region 

 four easily recognized fault localities: One near the termination of the 

 Niobrara just north of Bear Creek; a second in the isolated Dakota hill 

 2 miles south of Clear ('reek; a third near the southern end of the Dakota 

 hogback first north of Golden; and a fourth one-half mile to the south of 

 the latter, near the line of union of the lower and upper divisions of the 

 Trias. The faults of each region have the present appearance of approxi- 

 mately east-and-wesl cross fractures, along which the ends of the upturned 

 strata are thrown to one side or the other. In the southern half of the 

 held the northern ends of the interfault blocks are carried westward, while 

 in the northern half it is the southern ends that are carried westward. The 

 fractures in the isolated Dakota hill south of Clear Creek are irregular and 

 apparently local in their character. As a rule, the extent of throw of the 

 faults mentioned is slight and is confined to a single formation, one frac- 

 ture only — of the group in the southern portion of the area — extending 

 beyond 100 or 200 feet, this including the Niobrara, Benton, and Dakota, 

 luil being much less pronounced in the older formations than in the 

 Niobrara 



The faults in the vicinity of the Ralston dike and the foothills of Coal 

 ('reek will lie discussed in a separate section. 



