296 G. D. LOUDERBACK — STRUCTURE OF THE HUMBOLDT REGION 



fossils have been found either in the Humboldt range or in any range 

 in its vicinity. 



The character of the rocks of the Humboldt Lake range indicates, in 

 general, comparatively shallow sea deposits. Pure limestones are rare 

 and occur in thin layers. The most common type of limestone is argil- 

 laceous, and gray to black in color, but arenaceous limestones, limestone 

 breccias,* limestones containing pebbles, oolitic limestones, gypsum, 

 slates, and quartzites, all testify to the terrigenous or shallow water 

 character of the greater part of the deposits. 



Folding. — High angles of dip in various directions predominate in the 

 bedrock complex. The major folds are generally open, but not sym- 

 metrical ; the minor and subordinate folds are irregular, often overturned, 

 and sometimes sheared. 



The largest fold in the vicinity of the section studied is the Muttleberry 

 anticline. Along the Muttleberry road this includes all of the exposed 

 bedrock series. Near the mouth of the canyon at the west base of the 

 mountains the slates give fine exposures, striking roughly along the 

 range and dipping about 50 degrees west. Farther up the road are 

 quartzites and fossiliferous limestones, varying somewhat in dip and in 

 places corrugated, but with a decided general inclination to the west 

 until near the summit of the road, when the dip flattens until almost 

 horizontal. A short distance along the trail, east of the road summit, 

 the rocks become vertical, and not far beyond are covered with later 

 volcanics. They do not crop out again on the east side. Plate 16, figure 

 2, shows this anticline in section. The horizontal distance from its last 

 western exposure to the axial line is about 2 h miles and the vertical 

 distance 600 or 700 feet. It is distinctly unsymmetrical. 



The Muttleberry anticlinal axis as it passes north trends somewhat 

 eastward across the range, and a mile or two north of the canyon it is 

 followed at the west by other folds. In a section passing through the 

 gypsum deposits a couple of miles north of the mouth of Muttleberry 

 canyon it is followed by a syncline and then another anticline. 



The minor folds are more complex than the major one. At the gyp- 

 sum deposits above referred to the southern part is folded into an un- 

 symmetrical anticline, with its steep limb on the west. The northern 

 part is folded into an unsymmetrical syncline, with its steep limb on the 

 east. It has been brought approximately to the level of the southern 

 anticline by a thrust. 



An overturned and sharply bent fold is well exposed in Smith's wood 

 canyon, just north of Muttleberry canyon. 



* This refers to limestones brecciated in original formation and not to those secondarily brecci- 

 ated by pressure, as described on page 298. 



