GEOLOGY OF THE LARAMIE PLAINS 



a broad summit and an altitude of 7,800 to 8,300 feet above 

 the sea, with only one peak as high as 9,000 feet. 



"The drainage from the Laramie Hills is all eastward and 

 no streams flow west, with a few springs at the base of the hills 

 that afford a small supply of water. " 



"There are but few trees on the summits, with some pines 

 in the valleys and on the slopes. 



"The Laramie Hills form a single anticlinal range, its central 

 mass a heavy body of metamorphic granites of Archean age, 

 with Paleozoic rocks on the flanks resting at 4° to 1 0^ against 

 the west side of the slopes." 



Hayden in his report, 1867-1869, says that the Laramie 

 Range forms one of the most complete and beautiful anticlinals 

 seen in the Rocky Mountains. It extends from a point near 

 the Sweetwater, southeastwardly, curving around until lost in 

 the main range near Long's Peak, but Hayden considers the 

 Laramie Plains to be not over 100 miles long. The nucleus 

 of the Laramie Hills is red syenite, flanked on each side by 

 Paleozoic and Mesozoic, with Tertiary in some places, inclin- 

 ing at different angles. A vast deposit of Cretaceous and Ter- 

 tiary was formed in this region with a small percentage of 

 calcareous material. The Cretaceous amounted to 5,000 feet. 



Clarence King in the "Geology of the 40th Parallel" con- 

 siders the Medicine Bow granite later than that of the Colorado 

 and Laramie. The extension of the Medicine Bow south of 

 Wyoming is o\erflowed by a rhyolite mass. Medicine Peak 

 consists chiefly of white quartzite nearly 2,000 feet thick, trending 

 north 20*-^ to 25^ east and dipping east, the quartz being 

 cut by a dioryte dyke. In the rocks of the Laramie and Medi- 

 cine Bow are found quartz, orthoclase, plagioclase, hornblende, 

 mica, chlorite and calcite. In other respects the ranges differ. 



.S.") - 



