384 M. R. Thorpe— The Abajo Mountains, Utah. 



Structural Valleys. 



The major stream channels, carved in sedimentary 

 strata, have been determined by synclinal valleys. Near 

 the head of Johnson Creek on the east bank, the Dakota 

 sandstone dips 26° ± SW, strike N. 45° W., while in the 

 bed of the creek near this point, the strata of the McElmo 

 formation dip 6° S, strike E-W and on the west side of 

 the creek the Dakota dips southeast at varying angles. 

 North Canyon is another syncline, the floor of which is 

 Dakota sandstone. On the east side of Horsehead Peak 

 the strata dip to the east at high angles, slopes of 45° 

 being common, while in the creek bottom they dip down- 

 stream and on the east side of the canyon are steep 

 westerly slopes. Indian Creek has cut through the 

 Dakota and McElmo formations along a line of weakness 

 due to faulting caused by the uplift of North and Shay 

 Mountains on opposite sides of the creek. 



Floor. 



The floor of the Abajo group is slightly visible in two 

 localities; one in Hop Creek on the northwest slope of 

 Mt. Linnaeus and the other in Recapture Creek. Both of 

 these exposures are very much obscured by talus and do 

 not furnish sufficient data for a definite statement that the 

 floor or floors is or are even or uneven, but in the writer's 

 opinion they are uneven for the following reasons : 



1. In this system there are a group of laccoliths, with 

 both vertical and horizontal distribution, as determined 

 from their position and structure. Hence part of the 

 floor of one is the uneven roof of the laccolith next below. 



2. The general structure of the region shows folding 

 and faulting near the Abajo area and it is now generally 

 agreed that very little, if any, of those phenomena have 

 taken place since the uplift of the group. 



3. Hay den, in a section through this area, constructed 

 after his studies in 1876, drew an uneven floor with the 

 west side much higher than the east. 2 



4. There is a difference in elevation between the same 

 horizons on the west and east sides of the group of 

 between 1,500 and 1,750 feet, the higher level being invari- 

 ably on the west. Emery noted like evidences of the ante- 

 cedent structures in the Carrizo Mountains. 



2 Hayden, F. V.: Geol. and Geog. Atlas of Colorado and portions of 

 Adjacent Terr. 1877, Sheet XVII, sections to accompany Sheet XV. 



