4o8 



University of California. 



[Vol. 2. 



the underlying Campari conglomerates, and two lie entirely within 

 the area of these conglomerates, reposing directly upon them. 

 Four rest on the basalt alone, viz., that which forms the summit of 

 Little Grizzly, the area about 1,500 feet to the west of this, one on 

 the western flank of Gopher Ridge, and one on the north slope of 

 Rough Hill. The smallest area lies above the county road on the 

 east side of Wildcat Creek. It rests upon a small area of basalt, 

 and the latter directly upon the Grizzly Peak andesite, the older 

 formations of the Campan series being wanting. 



The distribution of these various residuary patches of this 

 rhyolite agglomerate and tuff show that the underlying basalts 

 had been subjected to extensive erosion before its deposit. The 

 basalt was undoubtedly originally much more extensive than it 

 now is, and yet its present boundaries were approximately defined 

 by erosion before the accumulation of the agglomerate and tuff 

 above it. We are, therefore, warranted in the inference that a long 

 interval of time intervened between the two extravasations. 



Later Faulting. — Since the deposition of the agglomerate and 

 tuff formation, the Campan trough has again been disturbed and 

 broken by faults. Two of these faults are important structural 

 features of the Campan series. One serves as the northern limit 

 of the Rough Hill area of agglomerate, the latter having been 

 dropped below the basalts against the tuffs which underlie them. 

 The other serves as the northern limit of the Campan volcanics, 

 these having been dropped on the south side of the fault against the 

 underlying Campan conglomerates. This fault appears to swing 

 around and to be continuous with the fault which dislocates the 

 Campan volcanics and sedimentary beds to the east of Pie Knob 

 as it is indicated on the map. Other small faults to the south of 

 Pie Knob, rendering the structure complicated and giving character 

 to the geomorphy, are probably of the same age as these two 

 larger faults. 



This summary account of the formations which make up the 

 Campan series, as left to us by erosion, suggests the possible 

 existence of still other formations once above the rhyolite agglom- 

 erate but now entirely removed. The fragmentary condition of 

 the latter formation, although comparatively hard and resistant to 



