GEOLOGICAL SURVEY OF THE TERRITORIES. 121 



CHAPTER X. 



THE LARAMIE PLAINS. 



In our last chapter we descended the western slope of the first moun- 

 tain range to a broad, open expanse of mountain prairie known as the 

 Laramie Plains. This great area might be called a park; it is enclosed 

 on three sides by extensive mountain ranges, but on the west its limits 

 are not well defined, inasmuch as no mountain ranges of any importance 

 intervene until we come to the Wasatch range, in Utah. It is usually 

 understood to extend westward almost to the Medicine Bow River, and 

 thus comprises an area about fifty miles from east to west, and one 

 hundred from north to south, the Laramie range or Black Hills forming 

 the eastern boundary. As we ride on the cars through the plains, these 

 mountains, with their comparatively uniform and gently sloping sides, 

 seem for many miles to bend around so as to inclose us within their 

 walls. On the south side are the Medicine Bow Mountains, which are 

 far more formidable and lofty than the others; indeed, the ranges this 

 side are quite irregular and fragmentary, and are known by different 

 names, as Sheephead Mountains, Elk Mountains, &c. Many of these 

 lofty peaks and ranges have not yet been explored geologically or geo- 

 graphically, and these magnificent fields are ripe and waiting for the 

 harvest of science. The far West is vast, but the laborers are few. 



Before proceeding, we might for a moment trace to their sources in 

 the mountains some of the beautiful rivers that wind their way through 

 the plains. We shall find to our surprise that, although we have crossed 

 a range of mountains the highest along the line of the road, we are still 

 in the great valley of the Platte in which we started on our journey. 



The main branch of the North Platte rises in the range of mountains 

 which forms the north side of the Middle Park, very near Long's Peak. 

 It takes a course a little west of north, flows through the middle of the 

 North Park, cutting its way through immense canons between the 

 North Park and the Laramie Plains. It then continues nearly a north 

 course, through tertiary as well as cretaceous rocks, to its junction with 

 the Sweetwater, where it bends around to' the east, so that near the Red 

 Buttes its course is nearly southeast until it reaches the main Platte, 

 near longitude 101°. 



The Sweetwater, which is the principal branch of the North Platte, 

 rises in the southern end of the Wind River Mountains, and flows nearly 

 east and unites with the North Platte near Independence Rock. These 

 streams flow through nearly every variety of geological formation 

 which occurs in the West. From the junction of the Sweetwater to the 

 Red Buttes it flows through granite, carboniferous limestone, red beds, 

 Jurassic marls, and White River tertiary beds; and from the Red 

 Buttes through lignite tertiary to a point about one hundred miles 

 northwest of Fort Laramie. There the White River tertiary beds over- 

 lap the lignite tertiary, and then continue to the forks of the Platte. 



The Medicine Bow and the two Laramies are important branches of 

 the North Platte, and take their rise in the lofty, snow-capped mountains 

 on the south side of the Laramie Plains. The region north of the North 

 Platte is mostly a vast sage plain, and but few small branches flow in 

 from that direction, but a multitude of small streams cut deep channels 

 through the sides of the Laramie range and flow into the North Platte. 



From Red Buttes to Fort Laramie, a distance of one hundred and fifty 

 miles, many beautiful little streams rise in the Laramie range and pour a 

 good volume of water into the Platte. These creeks occur every few 



