90 DESCiilPTIVE GEOLOGY. 



These yellow marls stretch off to the north with a low dip of 3° or 4° ; the 

 Colorado group extending northward beyond the limits of our map. 



Still farther westward, the Colorado group forms the surface formation, 

 inclined at a gentle angle, and presenting but little of special interest. 

 Between one and two miles east of Como Lake, they begin to show a higher 

 dip, and to indicate the structural features produced by the Como Ridge, 

 a somewhat singular uplift of the lower Mesozoic strata. 



Como Anticlinal. — Como Ridge is situated in the extreme northwestern 

 corner of the Laramie Plains, just west of the 106th meridian, and along the 

 northern border of the map, the boundary-line cutting through Como Lake. 

 The ridge, which takes its name from the lake, derives its importance solely 

 from the geological interest which centres in the region, where it forms the 

 southern side -of a local anticlinal axis. The upper Cretaceous beds form 

 the overlying strata of the plains over wide areas; but here, at Como, the 

 lower rocks down to the Red Beds are exposed in a gentle uplift, the later 

 beds dipping away in all directions. The main elevating force has acted 

 approximately in an east and west direction, producing an anticlinal ridge, 

 with its southern side again lifted up above the main axis of elevation. 

 Directly along the axis of this fold lie the Jurassic marls and soft friable 

 sandstones, which have undergone considerable erosion, leaving a shallow 

 basin now occupied by the lake and a narrow anticlinal valley. On the 

 south side of the lake, through the valley, runs the railroad, beyond which 

 stands the main ridge, forming the south side of the fold. This ridge rises 

 between 200 and 300 feet above the level of the lake, with a steep mural 

 face toward the north, but falling off gently on the opposite side. On the 

 summit, the ridge has a strike of north 60° east, with a uniform dip of 20° to 

 25° to the southward. Southeast of the lake occur the lowest beds exposed, 

 which consist of hard yellowish-red sandstones, and may belong to the 

 uppermost members of the Red Beds, or may simply be a compact reddish 

 stratum in the Jurassic. On account of this doubt, the Triassic formation is 

 not represented on the geological map, although it is not at all improbable 

 that the lower red sandstones should be so referred. 



Directly overlying these red sandstones occur well-defined Jurassic 

 strata, which form the northern face of the ridge, and are in turn overlaid 



