FORMATIONS OF THE FRONT RANGE 417 



vicinity, this unconformity at the base of the Morrison comprises all 

 Permian, Triassic, and Jurassic times. Some features of the Red beds 

 along the Rock} 7 Mountain front range are as follows : 



Near the Wyoming state line the lower sedimentary rocks consist 

 largely of limestones, which extend south from Wyoming, overlain by fine 

 grained, gypsiferous red sandy shales (Chugwater formation), which are 

 capped unconformably by the Sundance formation (marine Jurassic). 

 These limestones give place rapidly to coarse sandstones, mainly of red 

 color, which extend for many miles south as the basal member of the 

 sedimentar} 7 " series. At the top of these coarse beds there is always, in 

 northern Colorado, a body of finer grained, regularly bedded sandstone 

 from 50 to 200 feet thick, varying in color from gray to red, which ap- 

 pears to be an extension of the Tensleep sandstone. 



The most northern exposures which I examined in Colorado were in 

 Owl canyon, a small branch of the Cache la Poudre drainage, followed 

 by the old main road from Denver to Laramie. The section of the Red 

 beds in this canyon, 17 miles northwest of Fort Collins, Colorado, is as 

 follows : 



Feet 

 Gray shale and buff sandstone with Jurassic fossils 



Massive pale red sandstone, partly cross bedded 40 + 



Red, sandy shales with gypsum at top and thin layers of limestone near 



bottom 200 + 



Gray limestone, in part thin bedded .... 5 



Red sandy shales with several beds of gypsum near bottom 120 



Gray cross-bedded sandstone 15 



Red sandy shales with two thin layers of limestone 150 ± 



Pink sandstone, mostly fine grained, regular bedded 50 



Fine grained, light gray limestone 20 



Reddish sandstone . . . . '. 25 



Fine grained, moderately light gray limestone 15 



Reddish to buff sandstone 30 



Limestone 6 



Coarse red sandstone with red shale. 150 -f- 



Coarse reddish and gray conglomerate 100 ± 



Granite 



The massive reddish sandstone at the top of the Red beds in this sec- 

 tion is a feature which extends southward to beyond South Platte river. 

 It is overlain unconformably by the marine Jurassic at the north and 

 by the Morrison at the south. The local bed of coarse sandstone in the 

 Red beds is an unusual feature. The prominent limestone horizon is 

 believed to represent the Minnekahta limestone of the region north. 

 The 50-foot bed of pink sandstone at the base of the red shales is the 

 member previously alluded to as probably representing the Tensleep 



