By projecting the present slopes of the crater rim upward and making adjustments to conform to the slopes of similar volcanoes, it has been estimated that approximately 17 cubic miles of old lava has been removed, which formed the upper part of ancient Mount Mazama. _Toward the close of the activity forming the crater, minor eruptions produced Wizard Island and possibly other cones._—If the lake were removed, the crater would be seen as a relatively flat-floored cavity extending as a maximum about 2,000 feet below the present lake surface. In this great depression Wizard Island would appear as one of perhaps several volcanic cones produced by pouring out of lava and cinders in the last period of volcanic activity. Forming of the present floor probably involved many stages, during some of which the cauldronlike crater may have been occupied by wide stretches of molten lava, as in the “lake of fire,” at Kilauea, in Hawaii. _Origin of the lake._—The water of Crater Lake is derived from rainfall and snowfall over this crater region, together with snow blown into the depression. The lake is not known to have an outlet except by seepage. The conditions of evaporation, seepage, and precipitation are in a state of balance which makes possible this accumulation of water and maintenance of approximately this water level. If the region were at a different altitude, or in a different location, the lake might not have been formed. It is conceivable that in the course of late stages in its history, and under climatic conditions different from those of the present, the crater may at times have been filled in part with ice. The existence of Crater Lake was made possible by the building of a mountain, in the elevated summit of which there could be formed a wide and deep cavity having no outlet, except by seepage, and no inlet. The conditions required for the accumulation of a body of water with the peculiar beauty of this lake are furnished in a crater produced by a combination of those tremendous forces found in the power and heat of a volcano. _Color an outstanding character of Crater Lake._—The color of Crater Lake is generally recognized as the most attractive feature of this region. Among spectacular lakes of the world there are none in which the depth of color and brilliance of blue are more striking. The blue of the deeper water is brought out in contrast with the brilliant green of shallow areas along the margin. The deep blue of the lake is believed to be caused chiefly by the scattering of light in water of exceptional depth and clearness. The color is thought to be due to the same cause that produces the blue of the sky where light passes through deep atmosphere. The extraordinary beauty of the lake arises in part from its great depth, the clearness of the water, and of the atmosphere above it, and from favorable conditions presented in viewing it from the high crater rim.