THE MORRISON FORMATION OF SOUTHEASTERN 



COLORADO 



A considerable part of southeastern Colorado and north- 

 eastern New Mexico is elevated to a height of about 5000 feet 

 above sea level. The streams of this region have cut canyons 

 to the depth of 700 feet or more. The most notable of these is 

 the canyon of the Cimarron in New Mexico, and that of the Pur- 

 gatory, or Las Animas, in Colorado. The studies of which the 

 conclusions are given in this paper, were carried on mainly in 

 the canyon of the Purgatory and its tributaries, although a side 

 trip was made to the canyon of the Cimarron. The region 

 examined is shown in the accompanying sketch map (Fig. 1). 

 The canyon walls are steep and bare and complete sections are 

 easily obtainable. The lower half is red sandstone overlain with 

 gypsum (the "Red Beds"); the surface rock is also sandstone 

 (Dakota.) Between this upper sandstone and the gypsum is 

 the shale formation of which I specially \yrite. The shales are 

 found throughout the region examined wherever the streams 

 have cut through the upper sandstone. 



Two detailed sections were taken at the points indicated on 

 the map by a cross (x), section 1, at the junction of Plum and 

 Chaquaqua canyons, and section 2, in Red Rocks Canyon. Since 

 the canyons do not cut entirely through the Red Beds at any 

 point within the area examined, it is impossible to accurately 

 estimate their full thickness ; the sections, therefore, represent 

 only the upper part of these beds. 



For some distance above the bottom of Plum Canyon (sec- 

 tion 1) the rock is evenly stratified, ripple-marked and some- 

 what shaly. A limestone layer four feet thick near the bottom 

 extends uninterruptedly for many miles and forms a convenient 

 line of reference. Above these evenly stratified beds occurs a 

 series of massive layers of coarse red sandstone aggregating 

 about 250 feet in thickness. This series forms the steepest and 



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