GEOGRAPHICAL SITUATION AND GENERAL CHARACTER 309 



more basic and basaltic than the others, and the analysis shows that it 

 is 10 to 12 per cent lower in silica. 



Geograpjiical Situation and general Character of the Region 



As shown on plate 37, the Leucite hills are situated in the south- 

 western portion of Wyoming between the exterior lines of ranges 101 

 and 105 and townships 20 to 23. They are a little north of the center 

 of Sweetwater county. They extend over a distance of 30 miles from 

 their eastern edge, Black Rock mesa, to their western representative, 

 Pilot mesa, and about 25 miles from the most southern to the most 

 northern exposures. The southern edge of the nearest exposure to the 

 Union Pacific railroad is about 10 miles north of the Salt Wells siding, 

 15 miles northwest of Point of Rocks,* and, with the exception of Pilot, 

 about 20 miles northeast of Rock Springs. From Point of Rocks and 

 Rock Springs there are wagon trails leading to Atlantic and South Pass 

 which pass the mesas, but Rock Springs is the best point at which to 

 outfit for a visit to them. At the same time, the Leucite hills cannot be 

 said to be easily accessible. The land is an arid desert except for a few 

 springs. There are no ranches among them, although a few horses and 

 cattle range them in summer, and in winter, when the snow furnishes 

 drinking water, sheep herders use both the mesas and the intervening 

 valleys as ranges. Despite the apparent aridity, there is much nutritious 

 bunch grass and excellent pasturage. Along the talus slopes cotton-tail 

 rabbits are abundant and sage hens frequent the neighborhood of the 

 water-holes. Yet an ordinary trip by daylight gives no conception of 

 the teeming life of the desert. One of our drives took us late one after- 

 noon across the sand dunes which lie south of Steamboat mesa and 

 which are 2 or 3 miles wide. A gale of wind was driving the sand before 

 it and smoothing out all marks upon the surface. Toward night the 

 wind subsided, and in the morning at 7 o'clock, when we again crossed 

 the drifting sand, there was hardly a square foot that did not exhibit a 

 track of insect, quadruped, or bird, although to all appearances the dunes 

 were almost devoid of life. 



It is a question whether Pilot butte (or mesa) is to be classed with 

 the Leucite hills. Doctor Cross makes a distinction. It is, however, 

 embraced in this general name by us. 



General Geology 

 In the midst of the Red desert there is a huge dome of Cretaceous 



* Point of Rocks is the name of the station, on the Union Pacific railroad, and is a small frontier 

 settlement of long standing. The post-office is, however, Almond, which name appears on our 

 map. 



