Crater Lake is formed from the collapsed caldera of Mt Mazama. The resulting lake is over 1000 feet deep and is fed only by rain and snow runoff from the caldera sides. It is considered to be the cleanest, purest lake in the world. Right now, in mid-March, the snow there is about 10 feet deep in places. The blue of the lake has to be seen to be believed.
The outer slopes of the remnants of Mount Mazama feed the headwaters of a number of rivers, among them the Rogue. About 30 miles from the caldera the Rogue drops into a collapsed lava tube. The entire river is compressed into a channel that is so narrow that one could almost step across it. The force of the river pushing through this slot is incredible.