224 GEOLOGICAL SURVEY OF THE TEEEITOEIES. 



large stream, flowing directly from the broad depression north of the 

 Tetons. No sedimentary rocks were seen in this region. Only scatter- 

 ing groves of aspens, pines, and spruces had been seen thus far ; but, 

 after crossing, we at once passed into dense bodies of pines and spruces, 

 large areas of which had long since been burned over and were mostly 

 grown up again with dense young pines, from one to six years old, and 

 smaller numbers of quaking aspens. The country is much cut uj) by 

 precipitous ^aiions, from 50 to 200 feet deep, with flat bottoms and 

 broad shallow streams, the smaller ones being dammed by the beavers 

 at short intervals. A few purple-n acred unios occur in these streams. 



Approaching the Spring Fork of Henry's Eiver, two buttes are prom- 

 inent, consisting of porphyries and loose-textured volcanic sandstone. 

 Their tops are much cut by ravines, with flat, grassy hollows at their 

 heads, which at first remind, one of craters; but closer examination 

 shows that these are not distinct volcanic cones, but are merely frag- 

 ments of the terrace-like mountain to the northeastward, which have been 

 cut off from it and left behind in the general erosion of the valleys. Ou 

 the slopes of one of these buttes we found a profusion of large, blue 

 huckleberries, growing on rather small bushes a foot or so high ; but 

 these were not again seen on the whole trip. A smaller trailing species, 

 however, forming a perfect carpet in the 0])en groves of pine and 

 spruce, and bearing a very small, deep-crimson berry, with a pleasant 

 acid flavor, now began to appear, and was afterward found abundantly, 

 through all the pine-country, until we reached Jackson's Lake, late in 

 September. 



Spring Fork, where we crossed it, is about 100 feet wide, and was then 

 carrying about 150 feet of water. Its banks are very steep, consisting 

 mainly of the drab and pink porphyries so common in this region, which 

 are here well laminated and nearly or quite horizontal. If Eaynolds's 

 distances and ours are both correct, our camp must have been about two 

 miles below the immense spring, described by him as leaping over a 30- 

 foot fall into the stream, and furnishing to it fully two-thirds of its 

 water as well as its name. This sudden increase would explain the evi- 

 dent inconsistency between the size of the stream and the apparent ex- 

 tent of its upper basin. We did not at the time understand our relation 

 to Eaynolds's route, or we should have tried to reach this spring. Start- 

 ing from this camp the next morning, August 5, the steep bank proved 

 too exciting for one of the usually most obstreperous of our mules, and, 

 in attempting to kick herself free from her pack, she lost her footing and 

 rolled down hill, turning five complete somersaults before reaching the 

 bottom, where she quietly went to grazing, with only one or two slight 

 scratches. For want of any other name, at the time, we called this, 

 among ourselves, the Mormon Mule's Creek. 



Shortly after leaving this stream, we found the soil becoming notice- 

 ably thinner, and masses of basalt began to appear upon the surface. 

 The loosely -jointed character of the basalt seems to have given to the 

 soil, as fast as it formed, a ready i^assage downward with the water of 

 rains and melting snows ; so that, in many places, broad surfaces of the 

 rock appear, with barely enough soil upon them to support a few small 

 herbs and grasses. The basalt is doubtless underlaid here, as it is else- 

 where, by sands and gravels, which not only readily absorb all waters 

 percolating through the crevices of the basalt, but also furnishes covered 

 passage-ways for the large streams which supply large springs, of which 

 there are many examples in this region besides the one just mentioned. 

 Timber is here more scattered and has suifered less from fire than, in 

 the tracts we had recently crossed. The basalt is much bulged up into 



