HOLMES] JUNCTION VALLEY. 45 



in Steep cliffs or bluffs, and dart slides of the finely-divided rock ex- 

 tend down the slopes. The drawing given in Plate XXIY will give a 

 good idea of their appearance, and the accompanying map will show their 

 location. Farther down, in the vicinity of the mouth of Hell Eoaring 

 Creek, there are other remnants, but evidently belonging to different 

 flows. 



A greater part of the drift-covered mesa that occupies the middle part 

 of the valley between Elk Creek and the bridge is underlaid by sheets 

 of basalt, and some idea of their extent and thickness may be obtained 

 from the outcropping ledges near the bridge and below. Although the 

 outlines are very indefinite, it is probable that the basalts of this valley 

 do not altogether occupy as much as one square mile of surface. The 

 thickness will i)robably reach 200 feet, but it may be that there are inter- 

 colated beds of sedimentary or alluvial deposits. There is no outcrop- 

 ping ledge more than 20 feet in thickness. On the side next the river, 

 just below the forks, there are some pretty well developed columns. 



In passing to the west from the bridge, we ascend the basaltic mass 

 by way of a rounded depression or notch in the east face. Wlien we 

 reach the highest level we find that there is a general but gentle sloi)e 

 toward the west. The whole surface is drift- covered. We are here 

 about 400 feet above the river. The capping of basalt on Junction 

 Butte is some 200 feet higher, and unless the sheet flowed upon an 

 incline, or has been subsequently tipped, must belong to a higher flow 

 than any other of the remnants of the valley. It is less than 200 feet 

 thick, and in color quite black. It breaks down in minute, irregular 

 blocks. 



I present in Plate XXIII a sketch of the valley, looking east from the 

 low rhyolite hill near Elk Creek. In the foreground we overlook the 

 rounded, drift-covered mesas of the middle portion of the valley. At 

 the right we see a small portion of the drainage of Elk Creek, connecting- 

 through the low pass (m) with the Lost Creek Meadows. At the extreme 

 right we have the border of the rhyolite plateau. Lost Creek descends 

 from the plateau at r. The course of the river may be traced, coming 

 fi^om the right, crossing the middle of the x^icture, and coming out to 

 the left. We look directly up the sinuous valley of East Fork (e), the 

 junction being at a. The granites are exposed in the sharp bluffs on 

 both sides. It will be seen that Junction Butte (d) rises from a drift- 

 covered mesa which lies between the two rivers. Beyond the butte, a 

 little to the right, is the point of Specimen Eidge (^), and beyond we 

 can see the ridge which leads back to Amethyst Mountain (e). Between 

 the higher j)art of the ridge and the canon there is a X)latean-like belt 

 on which there remains a portion of the great sheet of rhyolite {i) that 

 once extended across the space now occupied by the valley. The Ame- 

 thyst Eidge formed the northern border of the basin in which the 

 rhyolites were deposited. Tbc main body of the ridge is composed of 

 Tertiary strata and conglomerates. Xorth of the East Fork we have 

 rugged hills rising toward the mountains. 



In the drawhig 1 have indicated the trail, which divides in the middle 

 of the drift-covered mesa, the left branch crossing to the bridge and the 

 other turning to the right, crossing Lost Creek near W\q, bend of the 

 river and continuing up the west bank toward the mouth of Tower Creek 

 at li. In the wall which extends from & to ^ we have some of the 

 most puzzling phenomena of the region. The main formations of the 

 wall are rudely but horizontally bedded conglomerates, which, unfortu- 

 nately, I had no opportunity of examining closely. To all appearances 



