192 REPORT UNITED STATES GEOLOGICAL SURVEY. 
JOHN DAY BASIN. 
The area drained by John Day’s River comprises the extreme south- 
western portion of the district, the examination of which was limited, 
for want of time, to the eastern portion, or that drained by the East 
Tork. On the west a rather high and rugged mountain ridge (the Salt 
River ridge) intervenes between John Day’s and Salt rivers, shutting out 
the view of the valley of the latter stream. Along the crest banks of 
snow still lingered in shaded ravines as late as the middle of August. 
A few miles south of the Grand Caiion of the Snake and south of the 
water-pass of the John Day’s the high crest abruptly falls to a lower mount- 
ain ridge, which forms its continuation northward; to the south the 
mountain gradually rises in altitude, presenting a uniform ridge 10,000 
to 10,800 feet in height in the district explored the previous season by 
Messrs. Gannett and. Peale. The belt between this ridge and John Day’s 
ridge is occupied by a hilly basin holding many pretty little valleys and 
meadow basins. Both the John Day’s and its Hast Fork flow through 
willowy intervales hemmed by steep slopes. 
Descending the west flank of the John Day ridge, the upper siliceous 
deposits of the Carboniferous fall steeply, their débris strewing the slopes 
and burying the foot of the mountain beneath great piles of fragmentary 
materials. In the edge of the parallel depression more or less well-ex- 
posed Jura-Trias deposits may be traced both to the north and south, 
dipping uniformly westward, and occupying a belt one or two miles in 
width. Beyond lies a wider belt, 4 to 5 miles or more across, in which 
a heavy series of sandstone and clay deposits is met with, also dipping 
westwardly at angles of varying inclination. 
On the western border of the latter belt, in the vicinity of the ridge 
lying between the forks of the John Day’s, on which Stations X and XI 
were made, this series of beds, together with the Jura (?), is elevatel 
into a sharp anticlinal fold, with northeasterly dips of 50°, more or less, 
and much less steep westerly inclination. But ascending to Station XI 
ridge, the strata resume their westerly inclination, and from the crest 
they descend into a depression where the series impinge against the 
abrupt mountain barrier whose basis rocks consist of the heavy gray lime- 
stone ledges of the Carboniferous, overlaid by red sandstones probably 
belonging to the middle member of the same series. The latter deposits 
also dip westward in the direction of Salt River Valley, though in places 
they have been described as being much disturbed, as noticed by Pro- 
oe Frank Bradley in the lower portion of the Grand Caiion of the 
nake.* 
To the north, along the Snake, the Jura-Trias outflanks the John Day 
ridge, the Jurassic member of the group appearing in fine exposures 
made up of variegated clays, sandstone and limestone ledges, in the 
abrupt mountain slopes hemming the right bank of the river. Both 
formations occur along a little stream which rises in a lakelet on the west 
foot of the John Day ridge, a few miles to the north of Station VIII, 
gaining the Snake just below the last bend in its course through the 
Grand Cafion. The Trias here exhibits its typical lithology, consisting 
of buff and red sandstones, dipping off the Carboniferous mountain ridge. 
The Jura near the confluence of the streams exposes heavy beds of more 
or less indurated light drab calcareous shales and limestone, which afford 
abundance of Gryphea calceola. 
iaaydens United States Geological Survey, Montana, Idaho, and Wyoming, 1872, 
p. 
