536 E. BLACKWELDER GEOLOGY OP WASATCH MOUNTAINS, UTAH 



north of Ben Lomond Peak ("Willard Peak" of the 40th Parallel Survey 

 maps) ; thence it passes diagonally down the eastern slope, is tempo- 

 rarily concealed by wash along the east base near the little village of 

 Liberty, but rises again at a low angle into the summits of the spurs 

 northeast of Ogden. It crosses Ogden Canyon near the east end and 

 continues southward along the eastern slope of the range. Presently its 

 outcrop is shifted by the Huntsville fault westward to the base of Ogden 

 Peak; thence it soon disappears beneath Tertiary and later sediments 

 in the Morgan basin. The overthrust has not been traced farther south, 

 but it can be confidently predicted that a structure of such magnitude 

 must continue many miles before it dies out in that direction. Along 

 this great thrust-plane the Lower Algonkian formations, consisting chiefly 

 of slate and graywacke, with some quartzite, have been pushed up over 

 Paleozoic rocks. The maximum horizontal displacement is about 4 miles, 

 so far as exposed, but this is probably but a small fraction of its total 

 displacement. The inclination of the thrust-plane varies considerably 



CA RBOrt/rEROUS 

 C AMB R ( A n 



Figure 6. — Diagrammatic Structure Section of the Wasatch Range, in Ogden Canyon 

 Showing the succession of overthrvist slabs of Paleozoic and Proterozoic strata 



from point to point. Locally it is as high as 50 degrees, but in the moun- 

 tains northeast of Ogden it averages about 15 degrees. This has sug- 

 gested that the thrust-plane may have been folded at a later date, like 

 those of the southern Appalachians. Inasmuch as the overlying Eocene 

 beds are slightly folded in northern Utah, it is safe to say that the thrust- 

 plane has also been flexed to the same degree; but it is equally probable 

 that the overthrust was originally an undulating rather than a plane 

 fracture. This fracture is clearly exposed in Willard Canyon and is 

 there the only overthrust. It may therefore be called the Willard thrust. 

 In Ogden Canyon there are two other large overthrusts, but both are 

 of distinctly less magnitude than the great Willard thrust — if, indeed, 

 they are not actually branches of it. One of these has already been men- 

 tioned in connection with the hypothetical "Ogden" quartzite. This 

 overthrust arises from the Salt Lake plain east of the village of North 

 Ogden, mounts along the frontal spurs of the range, and then descends 

 into Ogden Canyon (see figure 5). Throughout this part of its course 



