WHITE RIDGE. 153 



of Four-Mile or Horseshoe Creek. In regard to its nomenclature, local 

 usage is somewhat perplexing. The stream itself, when it debouches on the 

 South Park, is called Four-Mile Creek. Its main canon is generally known 

 as Horseshoe gulch. At its head it divides into two branches ; to the north- 

 ern of these has been given the name of Four-Mile amphitheater ; the south- 

 ern branch heads in two adjoining cirques or amphitheaters, the northern 

 of which has received, from its strikingly regular and complete curve, the 

 name of the Horseshoe. (See Plate XVII.) 



This gulch, like those to the north, is glacier carved ; but the walls are 

 less steep, as the upturned edges of the stratified rocks have been more sus- 

 ceptible to subsequent abrasion, so that the talus slopes, covered with shrubs 

 and trees, reach a considerable height. The wide gulch above the fault 

 still has traces of lateral moraines along its sides. Where below the fault 

 it is carved out of the Archean rocks, however, theee have been earned 

 away by later erosion, the gulch being here considerably narrower. When 

 the valley opens out again near East Leadville and bends to the southward, 

 although there is moraine material on the lower slopes, the form of the 

 ridges is not sufficiently distinct to show whether they are the original 

 moraines or consist of rearranged material. On account of the importance 

 of the district, the sections exposed will be described at considerable length. 

 The appearance of the surface is shown in the accompanying sketches. 

 That given on Plate XVI shows the more prominent outcrops on the ridge 

 forming the north wall of Horseshoe gulch, from White Ridge, on the west, 

 to the crest of the anticlinal fold, east of the London fault. 



white Ridge. The southwest face of White Ridge, as shown in the sec- 

 tion, is a mass of White Porphyry. On its back and north and east slopes 

 lie strata of Weber Grits formation, whose lines of outcrop can be traced 

 as distinctly and regularly as those on the back of the Gemini Peaks Ridge. 

 Their dip, however, is proportionately steeper, since the distance between 

 the porphyry body and the line of fault is shorter. This dip, as shown 

 in the sketch, varies from 30 to 45, the latter being the angle immediately 

 above the White Porphyry, which to the eastward decreases gradually to 

 30, and then, in close proximity to the fault line, rapidly steepens to the 

 perpendicular. East of the fault the curves formed by the beds of the 



