WYOMING ROCKIES 



377 



SE END 

 WIND RIVER 

 RANGE 



TERTIARY INTRUSIVES 



FOLDED AND FAULTED PALEO- 

 ZOIC AND MESOZOIC STRATA 



': X 



HANNA BASIN 



Jj5 PRECAMBRIAN CORE EXPOSED 

 --''I BEFORE BURIAL 



RAWLINS 



"n* 



Fig. 24.12. Laramide Sweetwater Range and Late Tertiary normal faults. Somewhat after Black- 

 stone, 1951. Thick hachured lines are the Late Tertiary faults. All others are Laramide. The range 

 ': subsided and was covered by Mid-Eocene, Oligocene, and Miocene sediments and volcanics. 

 Later erosion has exposed many peaks of the old range which are called the Granite Mountains. 

 The Hanna and Wind River basins contain thick Early Tertiary deposits. 



ders of the Precambrian core into a jagged pattern with a decided north- 

 west fabric. It is clear that the range was elevated in the general Laramide 

 revolution, and that the sedimentary veneer and probably much Precam- 

 brian rock was removed before the range started to sag. It was a singular 

 phenomenon in Wyoming and Colorado, because all other Laramide 

 ranges have remained as strong relief features until today, but similar to 

 a Laramide uplift in southwestern Montana. By the time of maximum 

 volcanism in the Absarokas, and at the time the Great Plains became a site 

 of sedimentation, the Sweetwater Range, although still possessing sharp 

 relief, had sunk to such an extent that it was being covered by shales, tuffs, 



and sands. This was in Oligocene time. A few remnants of Miocene beds 

 suggest that deposition continued beyond mid-Tertiary time, and cer- 

 tainly the entire range was buried. Then erosion set in, and many of the 

 granite peaks and flanking sedimentary ridges of the old range were re- 

 exposed. The stream pattern, as established on the Oligocene and Miocene 

 beds, became superposed on the Precambrian, Paleozoic, and Mesozoic 

 rocks, and the several examples of gorges through the islands are thus 

 explained. The history of burial is detailed under the headings, Hanna 

 Basin and Wind River Basin. 



The Sweetwater Range first rose in Fort Union ( Paleocene ) time and, 

 immediately afterward, was thoroughly eroded during early Eocene, was 

 partly buried by the Wind River beds, and then sank appreciably in late 

 Eocene time. 



The islands are in three rows today, the northern reflecting several 

 northwestward-trending anticlines and synclines in the Paleozoic and 

 Mesozoic rocks of the north flank of the range (see Tectonic Mop of the 

 United States), the central all in the Precambrian core, and the southern 

 revealing southward overthrustins; of the Precambrian rocks over the 

 sedimentaries. 



WIND RIVER BASIN 



The Wind River basin rests between the Wind River and Sweetwater 

 ranges on the southwest and south, and the Absaroka, Owl Creek, and 

 Big Horn ranges on the north. The basin is sometimes construed physio- 

 graphically to cover the former site of the Sweetwater Range because of 

 the low relief there. 



Details of the basin are best known from the work of Love ( 1939) at 

 the west end, Tourtelot and Nace ( 1946 ) at the northeast side, and Van 

 Houten (1957) on the south side. Love's work has already been sum- 

 marized in connection with the Absaroka Range. The Tertian* formations 

 of the basin are shown in the chart of Fig. 24.5. They range in age from 

 Paleocene to Oligocene, and in parts of the basin they may be over 10,000 

 feet thick. The basin is asymmetrical with the axis near the north margin. 

 The two chief structural variations from gentle basinward dips in the 



