The “desert” was formed about 7,700 years ago when a massive stratovolcano, Mt. Mazama, errupted in central Oregon. (For a brief history of Mt. Mazama, see my previous post, Vacation in a Volcano.) The pumice shown here is said to be up to 200 feet deep in places, and the surface has some grasses beginning to take hold. Only a few lodgepole pines have managed to eek out a living in this nutritiously-void soil. To visualize how this deposit came to settle on Mt. Mazama’s lower flank, imagine a debris-cloud of gas, dust and light-weight rocks blowing out of its crater and then rolling down the volcano’s slope where it then settled. You can infer the limits of the pumice deposition by interpreting the heavy tree line as its boundary — beyond the tree line, fertile soil supports an entire pine forest that lies at the volcano’s base, encircling it. Even further in the distance, you can see the southern exposure of Mt. Thielsen. On our visit, we spent the first night camped outside the Park proper, at Diamond Lake, which has a magnificent view of Mt. Thielsen’s western flank at sunset. This “mountain” is really the congealed 250,000-year old innards of an extinct shield volcano that was carved and re-worked by the craggy artistry of advancing glaciers. Of course, some people today have different ideas about its usefulness.