PHYSIOGRAPHY OF BISHOP CONGLOMERATE 609 



of Zirkel Mesa has an elevation of 7,900 feet, 300 feet higher than 

 that of Zirkel. Most of the flows which are discordant are smaller 

 and lower than the average and evidently were poured out after the 

 principal period of extrusion on a surface somewhat reduced by 

 erosion. The larger of the Leucite Hills lava-flows do not differ 

 more among themselves as to elevation than do different parts of 

 the Miller Mountain plateau itself. 



Monadnocks. — Aspen Mountain which rises about 1,000 feet 

 above the level of the plateau to the south is a ridge of resistant 



Fig. 5. — Antelope Butte, a monadnock on the peneplain southwest of Aspen 

 Mountain as seen from a distance of three and one-half miles. To the right in the 

 middle distance is the head of a stream- valley which is working back into the plateau. 

 This view gives a fair idea of the appearance of the surface of the plateau, though 

 it is here somewhat less even than usual on account of proximity to the invading 

 stream-valley. In the immediate foreground is a smaller monadnock similar to 

 Antelope Butte. (Photo, by A. R. Schultz.) 



quartzite formed by the impregnation with silica of a soft Cretaceous 

 sandstone. On account of its superior hardness it stands as a 

 monadnock on the peneplain. From the summit of the mountain 

 there is on the north a steep drop to the lowlands of Bitter Creek, 

 and to the south a gradual slope to the surface of the gravel plateau. 

 At the time of planation Aspen was reduced to a moderate slope. 

 The present steep slope on the north side of the mountain is the 

 result of more recent erosion. 



Six miles southwest of Aspen is a much smaller monadnock 

 known as Antelope Butte which rises as a conical hill about 

 150 feet above the surface of the peneplain. Fig. 5, a view taken 



