62 GEOLOGICAL SUEVEY OF THE TERRITORIES. 



obtained. Weathered into the nsual forms produced by alternate hard 

 and soft beds, it begins at the top, by an escarpment of the yellow 

 sandstones of No. 1, passing down into purplish and greenish grays, 

 broken by darker lines of outcrop, each of which gives a tinge of its 

 own color to the already highly-tinted slide, and still farther down the 

 wide band of rich yellow transforms all to its own hue, and the whole 

 sweeps down like a gorgeous curtain over the bright red cliffs of 

 the Triassic (?). The closest search developed no trace of fossils, and 

 it is of course impossible to define the limits of the several periods. 

 The lithologic gradation here, from the Jurassic down through the 

 " Eed Beds " into the well-established Carboniferous is most perfect, and 

 the entire absence of fossil-remains leaves us without a clue. 



In passing up Rock Creek we descend through the strata and on either 

 hand fi^ud the caiion -walls composed of the red and maroon Carbonif- 

 erous series. On the left they support the Sopris mass, which stands 

 some miles back, and on the right rise into a cluster of rugged hills, 

 above and beyond which are the lines of Cretaceous outcrop, apparently 

 dii)piug to the westward. In the bottom of the caiion the maroon beds 

 seem, very oddly, to dip toward the Sopris uplift as if not affected by it, 

 but by some movement farther to the west, but they are doubtless folded 

 abruptly up against the northwest face of that mountain. Close under 

 the west walls of Sopris the creek forks. At this point the granite 

 appears, and may be seen, from far below, rising in rugged walls and 

 abrupt spurs. The two branches seem to emerge from the base of 

 these as immense springs, but by a closer approach we could detect the 

 caiions through which they flow. They are cut like great gashes through 

 the granite, having between them a high promontory. 



On the 30th of August we ascended this promontory, and found it to 

 be a very excellent point of observation (station 22). The peak lies to 

 the east, rising very abruptly from the creek and presenting an aston- 

 ishing mountain-slope. The creek-bed is 6,000 feet above the sea, and 

 the peak springs to the height of 12,800 feet in one jirecipitous, un- 

 broken slope, a rise of C,800 feet in one and a half miles. With the 

 exception of this western tongue, the granite mass seems to b,e a per- 

 fect cone that has had its apex pushed through the sedimentary strata, 

 lifting them up abruptly all around, but in no case affecting them out- 

 side of a radius of three or four miles. Indeed, if the erosion had been 

 more equal on all sides the exj^osed granite area must have been nearly 

 circular, but the great erosion of Eock Creek cutting so deeply into the 

 mountain-side, has developed an area something like that shown in 

 Fi"- 2 



This elevated area forms the extreme northwest end of the Elk range, 

 and is connected with the Capitol and Snoic Mass groups, which lie 

 about ten miles southeast, by a high, red ridge, the crest of an arch in 

 the Carboniferous rocks, which here connect completely across the 

 range. The more recent strata have been broken down and carried 

 away, so that their outcropping edges are ranged low down along the 

 flanks of the mountains, on the east side trending toward the north- 

 west, making almost a tangent with the Sopris granites, crossing Rock 

 Creek at the point where we entered the valley, and swinging around 

 to the north indefinitely, but, very probably connecting, in the low 

 couutry, with the corresponding series of the west side. 



The east branch of Rock Creek, which I have called Avalanche 

 Creek, heads in the northern and western faces of the Snow Mass 

 group, and has cut its way in a most remarkable manner down through 

 the side of the red arch, almost parallel with its crest, striking Sopris 



