374 CRATEE LAKE, OREGON. 



against the upper slope of the valley. Figure 11, from a color sketch 

 of the photograph from which figure 3 was prepared, shows the Llao 

 Eock flow distinctly. To the lake it presents a sheer cliff — that is, it is 

 abruijtiy cut off — and one wonders how much farther it may have 

 extended in that direction. Beneath the rock the outline of the valley 

 in cross section is evident, and it rests upon many layers of older lavas, 

 forming the rim down to the water's edge. The direction of flow in this 

 great lava stream forces us to believe that it was erupted from a large 

 volcano which once stood upon the site of the lake. Every layer of 

 lava in the rim is a coulee, dipping away from the lake. This is espe- 

 cially well shown in the canyon of Sun Creek, cut in its outer slope. 

 The sections of these radiating flows exposed upon the inner slope of 

 the rim all tell the same story as to their source. By projecting the 

 lavas in their course toward a common center we can reconstruct in 

 fancy the great volcano. Mount Mazama, which once occupied the place 

 of the lake, and, like Shasta or Eainier, formed a great landmark of 

 the region. Proceeding eastward from Llao Eock the rim loses some- 

 what in height, and at the head of Oleetwood Cove one sees the remark- 

 able spectacle of a lava stream descending the inner slope of the rim. 

 It is the only one that has behaved in this way, and its action throws 

 much light upon the disappearance of Mount Mazama. 



The Palisades are less than 600 feet in elevation above the lake, and 

 are composed almost wholly of one great flow. The streams of lava 

 extending northeast from this portion of the rim are broad and much 

 younger in appearance than those forming the great cliffs south of the 

 lake, where the flows are thinner and more numerous. 



Eound Top is a dome- shaped hill over the eastern end of the Pali- 

 sades, and is made up chiefly of the lava stream that formed the 

 Palisades, overlain by two sheets of pumice separated by a layer of 

 rhyolite. The upper surface of the Palisade flow, where best exposed 

 upon the lakeward slope of Eound Top, bears glacial striae, that extend 

 beneath the layers of pumice and rhyolite of later eruption from Mount 

 Mazama. It is evident from this relation that Mount Mazama was an 

 active volcano during the glacial period. The occurrence of eruptions 

 from a snow-capped volcano must necessarily produce great floods, and 

 these conditions may account in some measure at least for the detritus- 

 filled valleys of the streams rising on the rim of Crater Lake. 



Eeturning from this glacial digression to the boat trip on the lake, it 

 is observed upon the eastern side of the lake that Eed Cloud Cliff is 

 rendered beautiful by the pinnacles of reddish tuff near the summit, 

 where it is capped by a great, dark flow of rhyolite, filling a valley in 

 the older rim and extending far to the northeast. Here the springs 

 begin to gush from the inner slope and cascade their foaming rills to the 

 lake. They recur at Sentinel Eock, Button Cliff", and especially under 

 Eagle Crag, as well as farther westward. Their sources in many cases 

 can be seen in the banks of snow above, but in others they gush forth 



