140 SNAKE KIVER PLAINS OF IDAHO. [bill. 199. 
SAND DUNES. 
In general, sand dunes are absent from the Snake River Plains, but 
at a few localities some notable examples are present, In Snake River 
Canyon, to the south of the river and about 8 miles below Glenns 
Ferry, there are sand drifts of considerable size, which are conspicuous 
on account of their gray color, smooth bare slopes, and undulating 
crest lines. Again, in the extreme northeastern portion of the plains, 
between Camas Creek and Henrys Fork, there is an area of many 
square miles occupied by drifting sand which has partially buried a 
range of hills known as the Sandhill Mountains. This great deposit 
of wind-blown sand was visited by F. H. Bradley" in 1872, who 
described it as reaching a height of 250 to 300 feet on the hills and 
forming a barren belt about their sides and bases. To the west of the 
hills it covers a tract of country several miles wide, some of the drifts 
being from 100 to 150 feet high. This interesting region still awaits 
careful study. 
In many localities on the Snake River Plains where conspicuous 
sand drifts do not appear there is evidence that considerable surface 
material, mostly quartz sand, is traveling in the direction of the pre- 
vailing winds. The roads are sometimes rendered impassable by 
these small dunes. The manner in which the sagebrush checks the 
force of the wind and causes sand drifts to start suggests that if a 
tract about 100 feet wide should be cleared of brush on each side of 
a road, so as to give the winds a clear sweep, the sand obstructions 
would be removed. 
It is a noticeable fact that the well-delined dunes on the Snake River 
Plains are composed of sand from which practically all fine particles 
have been removed. The dust does not collect in drifts and ridges to 
a notable extent, but is deposited as an even sheet which, although 
thickest in the depressions, occurs on hillsides as well. The reason 
for this difference in the manner in which dust and sand is laid down 
is not apparent and would be an interesting subject for investigation. 
Along the border of flood plains of streams tributary to Snake 
River, and also on the surfaces of abandoned flood plains now forming 
terraces along the larger stream, water-laid soils occur. They are 
coarse or fine, according to the strength of the currents to which their 
deposition is due. Usually a variety of rock fragments is present, as 
along Snake River, but in the case of small streams there is less 
diversity and the debris is of the same character as the rocks forming 
the region whence the streams flow. Between Mountain Home and 
Boise the flood plains of the streams flowing from the mountains to 
the north are composed of angular granitic sand. Far out on the plain, 
where ephemeral streams expand and at times form playa lakes, the 
a Sixth Ann. Rept, U. S. Geol. and Geog. Snrv. Terr., 1873, pp. 211-212. 
