Numerous volcanoes were formed in this lava region during the relatively late outpourings of molten rock through small openings. The mass of these volcanoes represents only an extremely small volume in proportion to the total mass of lava. Mount Mazama at Crater Lake is one of these volcanoes, likewise are the volcanic cones of the Cascade Range. The more noted of these are Mount Rainier (14,408 feet), Mount Shasta (14,161 feet), Mount Adams (12,326 feet), Mount Hood (11,225 feet), Mount Baker (10,750 feet), Mount Lassen (10,453 feet), and Mount St. Helena (9,697 feet). The mountain in which Crater Lake rests was built principally by lava flows, poured out layer upon layer, and to a lesser degree by the piling up of volcanic ash, soil, and the deposits of streams and glaciers as they flowed down the mountain. At Dutton Cliff we see an example of successive layers of lava and volcanic ash. Near Discovery Point, in addition to layers of lava and volcanic ash, one may also see examples of glacial deposits and glacial striae or scratches. One can understand Crater Lake in its relation to the volcano only when the mountain is considered as the result of a building process extending over long periods in which many changes took place. The following is an explanation of some of the processes. _Lava outpourings through splitting of the mountain._—In addition to spilling out as broad flows of melted rock, it is common for the tremendous mass of molten lava in a volcano to break through the mountain side. The lava filling of such a crack or fissure is known as a dike. After it cools the material filling these fissures is often harder than the surrounding rock. Subsequent wash of water may cut away the softer bordering material, leaving the hard filling of the fissure as a sharp ridge. Devils Backbone, on the west side of Crater Lake, is an illustration of such a lava dike. _Action of streams and glaciers on the mountain in the course of its building._—In the section of layers forming the rim of the mountain we find evidences of wash by water. In some places this is shown by the cutting of valleys; at others, by the accumulation of water-carried ash, gravel, and boulders. Glacier ice carrying sand, pebbles, and boulders scratches or polishes the rock surface as it moves slowly over it. Glacial polish and thick beds of material carried by glaciers are common around the mountain. They are present on the surface rock and seem also to appear between earlier layers, showing that glaciers were present at various stages in the history of the mountain. Broad U-shaped valleys cut at various points around the crater are also characteristic of glacial action. Kerr Notch is such an evidence of glacial erosion. It was through a similar ancient glacial notch that the lava forming Llao Rock flowed.