bp.johs.1 WILLOW CREEK BASIN RIDGES. 351 



points the basaltic lavas reach high up on these volcanic crowned emi- 

 nences, where they may merge through gradations of more and more 

 vesicular varieties into the crowning scoriaceous deposits, and sloping 

 in every direction into the lower country. The occurrence and local 

 aspects under which these materials are observed, as also the sediment- 

 ary formations which form the basis of the basin ridges, will be briefly 

 noticed in the following summary of detail geology. 



WILLOW CREEK BASIN RIDGES. 



Situate between Willow Creek and John Day's Creek, the lowermost 

 ridge of the basin rises rather suddenly out of the volcanic upland that 

 slopes off its north and west flanks, and is thence continued southeast- 

 erly a distance of perhaps 12 mdes, when it flattens out into the low 

 basaltic plateau which intervenes between the west branch of Day's Creek 

 and the sources of the Blackfoot. Nearly the whole of the southern 

 half or two-thirds forms a broken ridge of basaltic buttes, to the north 

 rising into the rounded culminating summit on which Station XIV was 

 made, which attains an actual altitude of something above 7,400 feet. 

 This elevation is covered with red and dark scoriaceous lava debris, but 

 in the steeper break facing northward, heavy ledges of dark steel- 

 gray basaltic lava appear. The southwestern slope falls more gradually, 

 showing frequent exposures of similar volcanic ledges, dipping westerly 

 into Willow Creek Valley, as also inclining gently in the direction of 

 the open basin country to the south and west. This disposition of the 

 igneous rocks suggests the sources of the outflow in the neighborhood 

 of Station XIV, and it may be that the scoriaceous material belongs to 

 a remnant of crater effusions in which originated the blanket of lava 

 covering these elevations. But of crater cone, the imagination can dis- 

 cover in this eminence hardly more than a vague resemblance, and this 

 mutilated by time. The extreme southern end of the ridge presents a 

 limited tract of low, rolling hills, in whose smooth grassy surfaces ob- 

 scure exposures of reddish-tinted deposits were seen, which are probably 

 the reappearance in that direction of a similar series of deposits exten- 

 sively developed in the northern portion of this ridge. These low hills, 

 however, continue but a short distance when they are cut off by the 

 basaltic-floored plain lying to the south, southwest, and southeast. 



Xorth of Station XIV the ridge is almost dissevered by the erosion 

 of a little tributary gaining the east bank of Willow Creek, and which 

 occupies a small basin bordered by grassy acclivities which sweep up 

 into Station XIV on the south and the hills to the north which form the 

 northern continuation of the ridge. It is difficult to decide whether the 

 above mentioned depression is floored by the volcanics which every- 

 where occur in the adjacent plains. On the north side of the depression 

 the heavy bedded basalt gently rises up on the southwest flank, where it 

 culminates in the low cap of Station XV, 6,800 feet. But to the east the 

 bared southern slopes, exhibiting sedimentary deposits, rise rapidly into 

 a higher plateau, which, at Station XVI, a mile and a half north-north- 

 east of Station XV, reaches an altitude of 7,200 feet ; and about the 

 same distance north the sedimentaries cease in a somewhat higher hill, 

 the crest of which shows a heavy ledge of hard, drab, thin-bedded 

 trachytic rock, dipping at an angle of 40°, X. 30° E., the north and 

 northeast slope falling in rugged benches to the level of the basaltic 

 upland which extends down to the canon of John Day's Creek on the 

 one hand, and to Willow Creek on the other. 



In this latter cluster of hills an interesting series of sedimentary de- 



