ST. JOHN. ] WYOMING RANGE—HOBACK CANON RIDGE. 179 
10,450 feet, at Station VII near our south line. For convenience sake 
this ridge has been designated by the name John Day’s ridge. 
East of the latter point a high, undulating mountain plateau extends 
over to the Hoback Cafion ridge some 4 miles distant, and which forms 
a part of the mountain basin in which rise the East Fork John Day’s 
River and one of the tributary sources of the main Hoback. Geologic. 
ally, this basin forms the southern continuation of the valley between 
the middle and Hoback Cation ridges and is principally drained north 
by a lower south tributary of the Hoback, which gains the latter 
stream 2 or 3 miles below the cation. Thus limited it forms a narrow 
trough 20 miles in length gradually widening to the north where it is 
about 6 miles across, and is mainly occupied by Mesozoic and Tertiary 
deposits. The basin area to the west occupying the interval between 
the Salt River and John Day’s ridges, although much wider—10 to 12 
miles east-west—is very similar in geologic structure to that just men- 
tioned. 
The eastern barrier ridge of the range, which we have designated as 
the Hoback Caiion ridge, stretches due south from the south flank of the 
Gros Ventre Mountains to the south line of the district, a distance of 38 
miles. Although narrow, averaging 4 or 5 miles in width, it constitutes 
one of the most important topographic and geological features of the 
range in this region. In the northern half the Hoback River has opened 
a narrow way across the ridge nearly at right angles to its course, in 
which the geological structure of the ridge is well displayed. Between 
Hoback’s Cafion and the south flank of the Gros Ventre Mountains the 
ridge has an altitude of 10,000 feet; to the south of the cafon it gradu- 
ally rises, culminating in Hoback’s Peak {Station V1), a few miles north 
of the south line of the district, at an altitude of 10,800 feet above the sea. 
In the latter quarter it is broken by the canoned sources of Hoback’s 
River, and thence southward the water-divide is transferred to the middle 
or John Day’s ridge, which soon constitutes the main divide limiting the 
west side drainage of the Green River Basin in the district to the south. 
Throughout its extent this ridge presents from either side a very broken 
appearance, with steep, often precipitous, rocky acclivities, diversified 
by the rich color-contrasts imparted by the deep reds and drab browns 
of the Jura-Trias, the grays of the Carboniferous limestone, and the dark 
and light shades of the forest-covered and grassy slopes. | 
For so comparatively small area as that occupied by the Wyoming 
Range within this district, being only about 25 miles across and of an 
average north-south distance even less, it presents an exceedingly diver- 
sified surface and intricate drainage, with which are associated equally 
varied and interesting geological phenomena, which will be briefly dis- 
cussed in the following section. 
HOBACK CANON RIDGE. 
Along the eastern flank of the Wyoming Range there occurs a low 
outlying ridge parallel with and 3 or 4 miles distant from the Hoback 
Cation ridge, from which latter it is separated by the valley of tributaries 
which gain the Hoback a few miles above the cafon. This ridge is quite 
persistent to a point perhaps 7 miles north of our south line, where it is 
completely enveloped by the Tertiary deposits which here sweep high up 
on the eastern flank of the range, as will be noticed in a subsequent 
chapter devoted to the Green River—Hoback Basin. To the north of the 
Hoback the ridge, as such, is less well marked, being much eroded by 
Hoback tributaries descending from the south flank of the Gros Ventre 
Range, east of Station XII. 
