XX . LETTER TO THE SECRETARY. 



Idaho. Each was between 5 and 6 miles in length, about 2 miles of which appear to 

 have been measured directly, while the balance was ranged out by small, Avell propor- 

 tioned triangles. The expansions were by means of closed triangles, and apparently 

 were well executed. The astronomical connections were ample, consisting of stations 

 at Sherman and Fort Steele in Wyoming, Salt Lake City and Ogden, in Utah. These 

 points were located by the Coast Survey and by Lieutenant Wheeler of the Engineer 

 Corps. The scheme is well planned, most of the triangles being well proportioned, 

 and the only failures are unquestionably due to the incomisletenesaof the work, owing 

 to the abrvipt discontinuance of the survey. 



Since the discovery of the wonders of the Yellowstone country, in 1870, this region 

 has been a favorite field of exploration. Expedition after expedition has traversed it, 

 each following much the same routes as its predecessors, and, after the first, adding 

 but little to the sum of human knowledge regarding this strange fire-ridden country. 



The explorations in this region by this Survey, in 1871 and 1872, were singularly 

 prolific of facts, geological, physical and geographical, and little that was new was 

 evolved from numerous exiDsditions that followed. The big nuggets had been taken, 

 and nothing but a careful, scientific, reworking of the tailings would extract from them 

 the wealth of fine gold which they still held. 



In 1878, this Survey reached this region in the prosecution of its system of surveys. 

 Its work had, years previously, passed from the reconnaissance stage to that of syste- 

 matic surveys on a scale and of a degree of accuracy commensurate with the needs of 

 the country. 



In that year a party was directed to make a detailed survey of the Yellowstone 

 Park, its geography, geology and volcanic phenomena. 



A part of the results of this season's work is now before the world, in the form of a 

 map of the Yellowstone Park on a scale of two miles to an inch, a scale sufficiently 

 large to show all details necessary to the geologist or the traveler. The topograi^hy 

 is represented by contour lines, at approximate intervals of one hundred feet. This 

 map, as well as the others published by this Survey, are admirable illustrations of 

 relief-effect by means of contours ; and they not only express the relief, but the ab- 

 solute and relative elevations. 



From a study of this map, we find that the greater part of the surface of .the Park 

 consists of high rolling plateaus, broken by stream beds, cliffs and canons. Several 

 small groups of mountains diversify the surface, among them the Red Mountains, in 

 the southern part, rising 2,000 feet above the general level, or more than 10,000 feet 

 above the sea, and the Washburn group, near the middle of the Park. This group 

 has the form of a horseshoe, opening towards the east. The eastern border of the 

 Park is occupied by a high rugged range, to which has long attached the name of 

 Yellowstone Range. Index Peak, the highest measured peak in this range, exceeds 

 11,700 feet in height. In the northwestern corner of the Park is the southern extrem- 

 ity of the Gallatin Range, culminating in Electric Peak, a magnificent summit, 11,155 

 feet above the sea, which overlooks almost the whole Park. 



The mean elevation of this reservation apiiears to be not far from 8,000 feet, an ele- 

 vation so great in this latitude as to presuppose an almost arctic climate. The lowest 

 point within its limits is at the mouth of Gardiner's River, on the Yellowstone, which 

 is 5,360 feet. 



Marked features of the reservation are the low, indefinite divides and the abun- 

 dance of lakes and marshes. In several cases we note marshes extending across di- 

 vides and making "two ocean rivers," phenomena by no means as uncommon as are 

 popularly supposed. The lakes, principal among which are Yellowstone, Shoshone, 

 Lewis and Heart, cover nearly 200 square miles out of the total area of the Park, 

 which is estimated at 3,312 square miles. 



Many newly discovered groups of hot springs and geysers appear, for the first time, 

 on this map, among which should be mentioned the large and fine groups near the 

 head of Gibbon's Fork of the Firehole, the discovery of which has been previously 

 noticed. 



