64 
BULLETIN OF THE UNITED STATES FISH COMMISSION. 
The rim of the basin now occupied by Crater Lake is the present summit of what 
was once a mountain cone. That this is simply the frustum of what was once a com- 
plete mountain cone is evidenced by the attitude of the sheets of lava and ejected 
volcanic material which form the rim. They all incline away from the lake, indicat- 
ing a common source from a crater that surmounted a huge volcano high in air above 
the place now occupied by the lake. At that time, of course, neither basin nor lake 
existed. Mr. Diller thinks that this great volcanic mountain, recently named Mount 
Mazama, must have extended about 5,000 feet higher than the remaining fragment, 
thus making its height about 14,000 feet, nearly that of Mount Shasta. What became 
of the top of Mount Mazama is an interesting question. The geologists are convinced 
that at some period in its history the molten interior, instead of escaping through the 
crater in the usual way, found an outlet at a lower level. The top of the mountain 
being thus left a mere shell and without adequate support, fell in and became engulfed 
in the vast pit which the lake now partly tills. The pumice upon the surface for 
many miles around Crater Lake was probably blown out by the volcano before the pit 
developed, and the volcano of Wizard Island was active at a much later stage upon 
the bottom of the pit. It was the scene of the last eruption about the lake, and, 
although recent in appearance, must have occurred centuries ago. 
Crater Lake is, so far as known, the deepest lake in America. Many soundings 
have been taken by the United States Geological Survey. Over only very limited 
areas was a depth of less than 1,000 feet found, while over a large part of the lake the 
depth ranges from 1 ,800 to 2,000 feet. In the eastern portion of the lake is a great level 
floor, with a nearly uniform depth of 2,000 feet for a distance of more than 3 miles. 
In the western part are three or more small cones, one reaching within 93 feet of the 
surface of the water, while another rises 845 feet above the water. This is Wizard 
Island, a perfect cinder cone, with symmetrical slopes, and in its top a crater 80 feet 
deep. This cone is composed chiefly of red lapilli, and so new and fresh that it is 
sparsely forested and shows no trace of weathering. About the base of this island 
cone is a rough fringe of lava, which has spread in all directions to far beneath the 
water’s level. The shallowest parts of the lake lie west and south of Wizard Island. 
The average depth in this area probably does not exceed 150 feet. 
Crater Lake has neither inlet nor visible outlet. The catchment area is scarcely 
greater than the lake itself. During the summer season several streams trickle down 
the walls from the snow banks which lie within the rim; these streams are all very 
small, but a few of them continue throughout the summer, as some of the snow banks 
lying on the southern walls never entirely disappear. The amount of precipitation is 
believed to be greater than the evaporation, but the level of the lake does not appear to 
be rising. It is therefore quite probable that there is a subterranean outlet, and the 
large springs in the vicinity of Fort Klamath may have their source in Crater Lake. 
The water of Crater Lake is cold, fairly pure, and exceedingly clear. Though 
sufficiently pure for all fish-cultural purposes, it is slightly flat to the taste and doubt- 
less contains some minerals in solution. Froth or foam readily forms when the water 
is disturbed. The clearness is remarkable, an ordinary dinner plate being distinctly 
visible at a depth of nearly 100 feet, even in a hazy atmosphere. 
The color of the lake is a wonderful blue, except in certain comparatively shallow 
places near the shore. In the deeper parts of the lake it is the most intense blue we 
have ever seen ; from there toward the shore, and in the changing light and shadows of 
