188 REPORT UNITED STATES GEOLOGICAL SURVEY. 
its rise within the same basin on the extreme southern boundary of the 
district. This north-south valley belt has a length of about 25 miles 
from our south line to where it finally merges into the Snake Valley, 
in east-west extent ranging from 3 to 6 miles, approximately. It is en- 
tirely occupied by Mesozoic and Cenozoic formations, which uniformly 
incline off the Carboniferous in the west flank of the Hoback Cation 
ridge. Along the western border of the basin, or high up on the east 
flank of the John Day ridge, the strata have been faulted with down- 
throw on the east amounting to several thousand feet, so that the upper- 
most or latest of the geologic deposits impinge against the Carboniferous, 
which latter forms the crest of the ridge. 
South of the East Fork John Day’s River, which crosses this central 
mountain ridge in a deep eafion 4 or 5 miles north of our south line, the 
interspace between the two ridges is apparently occupied by Laramie, 
possibly also Cretaceous, deposits, which here hold a much higher actual 
altitude than is the ease farther north, the later formations having been 
removed to a large extent, at least, in this quarter. The exact line of 
the fault probably passes well to the east of the monoclinal crest of that 
part of the ridge south of the East Fork John Day’s River, which is made 
up of heavy deposits of hard light-reddish sandstone and gray lime- 
stones of the Upper Carboniferous. These deposits, which were identi- 
fied from specimens obtained at Station VIT by Mr. Clark, dip at a mod- 
erate and steepening angle of inclination to the westward, presenting 
rugged escarpments on the east several hundred feet in height. Hast 
of the heights the inferior limestone ledges rise up more gently in the 
same direction, appearing in long lines of step-like exposures in the high 
plateau of this part of the basin. 
In the divide north of the East Fork, however, in the line extending 
across from Hoback’s Peak (Station VI) to Station VII on the John 
Day ridge, the section discloses the entire Mesozoic series, as developed 
in this region, including above a heavy series of soft buff and gray 
sandstones and arenaceous clays probably referable to the Laramie. 
Two or three miles to the northeastward of Station VII a high outly- 
ing ridge, between the forks of the lower south branch of the Hoback, 
about midway between the Hoback Cafion and John Day ridges, is here 
crested with strata of the age of the Bear River Laramie. These con- 
sist of brownish gray and buff sandstones, dark blue, drab, and choco- 
late-red shales, with more or less indurated layers and occasional ledges 
of dark siliceous limestone. The latter beds at one point in this vicinity 
afforded a few fossils, Goniobasis macilenta White, Corbula pyriformis 
Meek? Pyrgulifera humerosa Meek, Unio vetusta M., &e., and obscure 
vertebrate remains, which identify the strata with the Bear River divis- 
ion. It is very difficult to estimate the exact vertical extent of this 
member, owing to the soft character of the beds, which readily yield to 
atmospheric erosion, and although the belt it occupies is exceedingly 
broken, few good exposures are to be met with. However, it probably 
reaches a thickness of several thousand feet, and is apparently conform- 
able to the Jurassic beds beneath. At the above locality the dip is 
westwardly at an angle of 35°, the intervening depression on the east 
being occupied by the Jura-Trias which rises up on the west flank of 
the Hoback Cation ridge, and which apparently folds round the south 
extremity of the ridge on which Station V was located. On the west, 
in the saddle reaching over to the John Day ridge in the vicinity of 
Station VIII, a heavy series of greenish gray and light buff sandstones 
and soft clayey deposits sueceeds, dipping uniformly westward, and 
reaching within 200 or 309 feet of the crest of the latter ridge, in abrupt 
