GEOLOGY — LASSEN'S BUTTE — CANOE CREEK. 



31 



The geology of all this region bears the record of intense and recent volcanic action. The 

 surface crossed before reaching the summit of the pass was covered with blocks of scoriaceous trap, 

 pumice, trachyte, or porphyry. The prevailing rock at the highest part of our route is a friable 

 felspathic lava, which readily disintegrates, forming a white sand, which reflects the sun 

 almost like snow. This rock is lying in rough and ragged masses, in many places bare of 

 vegetation, and of recent origin. 



lassen's butte, fbom the north. 



The open space about the base of Lassen's butte is doubtless due to the fires which, from time 

 to time, sweep through these pine forests, yet a large area in its vicinity is overspread with 

 volcanic products, evidently of so recent date that it seems not improbable that it has been in 

 a state of activity since many of the pines which are growing on its base began their existence. 



This accumulation of modern volcanic matter completely conceals all underlying rocks, and 

 gives an uninteresting monotony to the geology of the surrounding region. 



On Canoe creek, a tributary of Pit river, we found the first of the "Sage plains," which form 

 so constant a feature of the central desert. They here present arid surfaces of but limited extent, 

 bounded by cliffs, or ledges of trap, and covered with a light volcanic soil, which rose in clouds 

 of dust as we passed. Scattered bunches of grass, clumps of Artemisia, and a few trees of 

 yellow pine, comprise all the vegetation which their sterility does not exclude. 



As we descended Canoe creek we entered a region where volcanic phenomena are displayed on 

 an extended scale. 



This stream traverses a valley expanding towards the north, bounded by walls more than a 

 thousand feet in height, composed of dark lava-like trap or red scoria, the interval between them 



