THE RED BEDS OF THE FRONT RANGE IN COLO- 

 RADO: A STUDY IN SEDIMENTATION 



A. J. TIEJE 

 Berkeley, California 



Aim of this article. — The term "Red Beds," as used in this article, 

 needs some definition. The term includes only those Colorado for- 

 mations known as the Fountain, Lyons, and Lykins series and their 

 accepted time-equivalents east of the Continental Divide. These 

 beds lie unconformably on pre-Cambrian granites and gneisses,^ 

 occur more or less continuously from Wyoming to New Mexico, 

 and have an undetermined extension eastward from about lon- 

 gitude 105° W. They are tilted, often to angles of over 60°, the 

 direction of dip being southeast to east. The present paper is not 

 concerned with their age, already established by Henderson,^ the 

 Fountain and the Lyons as Pennsylvanian, the Lykins as Permo- 

 Carboniferous in its lower part, Triassic (?) in its upper part. 

 Rather, the paper aims to contribute to the literature of sedimenta- 

 tion by (a) fully describing the beds and (b) discussing both the 

 conditions under which the sediments were laid down and the pale- 

 ogeography at such times. Though the writer is familiar with the 

 "Red Beds" of the Black Hills, of the Bighorn uplift, of the Lar- 

 amie region, and of southeastern Colorado, the conclusions are 

 based chiefly on a two years' study of the stratigraphy from the 

 Cache la Poudre River, about 16 miles south of the Wyoming line, 

 to Canyon City, west of Pueblo. 



THE FOUNTAIN FORMATION 



Description. — It is difficult to give a typical section for the 

 Fountain formation because of its great lateral and vertical varia- 



^ At Canyon City the beds lie unconformably on Mississippian limestone and 

 overlap on Ordovician limestone. 



2 J. Henderson, "The Foothills Formations of North-Central Colorado," Colo. 

 Geol. Surv., Bull, ig (1920). Earlier discussions are chieflty by N. M. Fenneman, 

 "Geology of the Boulder District," U.S. Geol. Surv., Bull. 265 (1905), and R. M. 

 Butters, "Permian or Permo-Carboniferous," Colo. Geol. Surv., Bull. 5 (1913). 



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