28 CAKHONIKEROUS FORMATIONS AND FAUNAS OF OOLOHAOO. 



tills us (lie KIk Moiinluin region, restricting tlio iiiuiic (irarul HiNcr rcyioii to the 

 nortluTii portion. 



'I\) tli(> cast iuiil southeast oi' the (iraiid Kivor ami Elk Mountain areas, and 

 .separated In the Archean Sawatch Mountains, is a narrow and more linear 

 truet. the northern portion of whicli lies on the western side of the mountain 

 valley called .South Park. This, southward to the canyon of the Arkansas. I shall 

 designate the South Park region. 



Practically connected with this, but sending off a long spur to the northwest, 

 the outciop is taken up hy the Sangre de Cristo Range, and from the Arkansas 

 River southwanl to Costillo Peak, where the Carboniferous exposures cease, it may 

 be appropriately called the Sangre de Cristo region. 



Another well-detined area of Carboniferous rocks is found in southwestern 

 Colorado. This may be designated the San J uan area, and the Hayden survey has 

 several times employed for this general country the name Sun Juan region, or San 

 Juan district. Under this title will be included the Paleozoic series of the Rico and 

 the La Plata mountains, as well as the exposures in the valley of the Animas River. 



Another interesting series of outcrops occurs in western Colorado along the 

 lower portion of the Dolores River to its junction with the Grand, and along the 

 Grand from this point to beyond the State line in Utah. This series of outcrops, 

 because the name Grand River area has already been made use of, 1 will call the 

 Dolores River region. 



The last and final area is the entire strip of sediments upturned along the 

 eastern margin of the Front Range. The main portion of this outcrop, though 

 here and there containing patches of early Paleozoic beds, consists of the Red Beds 

 usually referred to the Trias; but their Trias.sic age is not well established, and 

 as reason exists for supposing that part of the series at least is of Carboniferous 

 age, I will speak of this as the Front Range region. This area will begin with the 

 northern border of the State and extend southward to the Huerfano River, including, 

 in fact, the boi'dering outcrops of the Wet Mountains as well as those of the Front 

 Range. 



All these areas have more or less extensive contiguous disconnected outliers, 

 but to these it did not seem necessary' to apply independent names, especially as no 

 evidence at hand demanded particular reference to them. Most of these areas are 

 artificial in delimitation and established for the purpose of convenience in ti'eatment. 

 The Uinta area is independent because of its isolated position, and because, perhaps, 

 of the peculiarities of its section. 



UINTA MOUNTAIN REGION. 



Perhaps the earliest geologic exploration in the Uinta Mountains, the earliest 

 certainly of which I have found note, was made by W. A. Jones," who traversed the 



CI Chief of Engineers U. S. Army, Rept. 'o;- 1.172. 1S73, pp. 1108-1118. 



