800 DESCRIPTIVE GEOLOGY. 



with perpendicular walls, Avhich render it peculiarly difficult to traverse, and 

 well fitted to a£ford secure refuge to the scattering bands of renegade 

 Indians, which frequent this region. Its physical aspect is most monotonous 

 and dreary, and it presents no inducements for exploration or occupation, 

 either for purposes of agriculture or of mining. The area represented on 

 the map constitutes the eastern limits or walls of the immense flows of 

 basalt, which extend more or less continuously westward into California, in 

 the region of the Upper Pitt River, and thence northward through Oregon, 

 east of the Cascade Mountains, and evidently stand in intimate connection 

 in geological history with the great basaltic flows which have built up the 

 Cascade Mountains, in the neighborhood of the Columbia River, and 

 covered so much of the interior valleys of that great stream. 



From beneath these flows, at intervals of 10 or 15 miles along their 

 southern and eastern edges, issue springs, which are of more than usual im- 

 portance on account of their rarity in this illy-watered region. The most 

 important are, that just west of the southern point of the Granite Range, 

 that at the Bufi'alo Station of the wagon-road, and the Sheep's Head and 

 Rotten Egg Springs along the western edge of the Mud Lake. According 

 to the Indians, there is also a spring of good water on the little basaltic 

 butte in the midst of the western Mud Lake. The Sheep's Head Spring 

 is remarkably picturesque, being a stream welling out of a circular orifice 

 of calcareous tufa about a foot in diameter. The Rotten Egg Spring, as 

 its name suggests, emits an .odor of. sulphuretted hydrogen. 



