SOUTHERN WASATCH MOUNTAINS, UTAH 441 
South Fork of Big Cottonwood Creek, where it appears to be over- 
ridden by the “upper” quartzite (the “Ogden” in the above table), 
which here rests directly, though discordantly, upon the lower 
(Cambrian) quartzite. The ‘lower’ limestone is absent to the 
northwest in Big Cottonwood Canyon. Southward from Alta 
the “‘lower”’ limestone extends in a synclinal attitude between the 
two quartzite belts as far as the head of American Fork Canyon, 
where it passes through a complication of faults and local con- 
tortions and finally merges into the great ‘“‘upper”’ limestone belt 
(see Fig. 2). Middle Cambrian fossils found by Mr. Butler in 
shale members of the ‘‘upper”’ quartzite both north and south of 
Alta confirm the structural evidence of an overthrust. These 
fossils were determined by L. D. Burling as follows: 
Zacanthoides cf. spinosus 
Obolus (westonia) ella 
Micromitra (Iphidella) pannula 
The overthrust structure, however, is complicated by two or more 
later fault systems. The older and more conspicuous of these was 
evidently developed by the stresses induced by the granite intrusion. 
The intrusion effected a domal uplift of the Paleozoic and Mesozoic 
rocks, and the force was great enough to rupture the dome in places, 
forcing the more central portions upward and outward against the 
outer portions. The strongest of these faults is best exposed on the 
north side of Little Cottonwood Canyon about half a mile west of 
Alta (Figs. 2 and 3), where the ‘“‘lower”’ quartzite and shale, badly 
contorted, abut against the “‘lower’”’ limestone along a steep 
westward-dipping fault plane. A second similar, but smaller, 
westward-dipping reverse fault is exposed about three-fourths of a 
mile east of the first, along the divide between Little Cottonwood 
Canyon and Mill D South Fork. The effects of these later reverse 
faults in obscuring the earlier overthrust are shown in Fig. 3. Both 
of the later reverse faults die out northward along the strike rather 
rapidly; southward the same, or similar, parallel faults are exposed 
near the head of American Fork Canyon, and the western one 
(nearer the granite) appears to continue in a southwestward direc- 
tion as far as the Silver Lake cirque, beyond which the quartzite 
belt is cut off by the intrusive granite. 
