Crater Lake National Park: Administrative History by Harlan D. Unrau and Stephen Mark, 1987

 INTRODUCTION: Description of the Park



While the lake and rim slopes are the primary resources of the park, there are a number of other significant natural resources within the park boundaries. In or near Crater Lake are reminders of the cataclysmic activity that once engulfed the area. These include the lava formations on Mazama’s sloping sides, extinct volcanic cones, and glacial valleys. Some of the more notable geological features of the park area are:

1. Wizard Island–Rising some 763 feet above the water, this island is an excellent example of the smallest type of volcanic cone. The summit of this perfect little cone is a crater about 90 feet deep and 300 feet in diameter. The cone and its massive flow of black lava in huge blocks form an island about three-fourths of a mile long by one-half mile wide. The oldest trees on the island date from about 800 years ago, indicating the last volcanic activity of Mount Mazama occurred about 1,000 years in the past.

2. The Watchman–A massive flow of andesite two-fifths of a mile wide and extending one and one-quarter miles downhill. It supports an impressive dike on the lake side.

3. Hillman Peak–The highest point on the rim, at 8,156 feet elevation, Hillman Peak was formed as a parasitic cone when a vent opened on the side of Mount Mazama. The collapse of the parent peak cut Hillman in half, exposing its inner structure. Its spires are ancient feeder tubes for the lava that built the cone and were decomposed and tinted yellowish-orange by the gases and other hot liquids that rose through them.

4. Devils Backbone–This is a vertical wall of dark andesite lining the cliff face and measuring about 1 ,000 feet long by 50 feet across near the top. A dike formed by molten lava that created and filled cracks, as it forced its way up through the rock and then solidified. It has been left standing by the erosion of the surrounding material.

5. Llao Rock–This great mass of dacite (a sluggish lava) was produced from a vent on the upper slopes of Mazama and hardened after moving only a mile or two. The dacite filled in a former explosion crater. This rock rises nearly 2,000 feet above the water- -the highest vertical precipice on the rim- -and was formed by the most massive single flow apparent in the caldera wall, with a maximum thickness of 1,200 feet.

6. Red Cone, Timber Crater–These are excellent examples of extinct cinder cones north of the lake, as is Crater Peak to the south.

7. Pumice Desert–A broad flat in the northern section of the park, this desert was covered with pumice and ash more than 200 feet deep in some places by the explosion of Mount Mazama. It has only started to be invaded by scattered lodgepole pines. Due to its scarcity of organic matter, few plants have taken hold to further enrich the soil.


8. Mazama Rock–This is a single huge block of andesite at least sixty feet high thought to have fallen from or been blown out of Mount Mazama. Erosion has removed surrounding materials.

9. Palisade Point–These are vertical andesite palisades covered with lichens.

10. Wineglass–This is a slide formation caused by erosion, that, when viewed from the opposite shore, resembles an enormous stemmed glass.

11. Redcloud Cliff–This portion of the rim shows seven distinct layers of glacial material, illustrating the relentless advance and retreat of glaciers on Mazama’s slopes.

12. Castle Rock (Pumice Castle)–Below Cloudcap a bright orange and pink formation of pumice and tuff protrudes from the caldera wall composed of layers of pumice laid down in the early days of Mazama and covered by later eruptions. Hot gases have colored them orange and apricot. Exposed during Mazama’s final collapse, they have since been eroded by wind and water into a formation called Castle Rock.

13. Mount Scott–This is what remains of a parasitic satellite cone of Mount Mazama that grew near its eastern base, presenting on the east a classic symmetrical volcanic silhouette. The western slope has been eroded by glaciation. It was built up before Mazama’s collapse and was probably a secondary vent during Mazama’s activity. Mount Scott is the park’s highest peak, at 8,926 feet.

14. Kerr Notch–Its U-shaped cross-section denotes the glacier that poured through the area and carved out Kerr Valley.

15. The Pinnacles–These towering needle-like formations of rock, called fossil fumaroles, projecting from the Sand Creek Canyon floor, were formed under sheets of volcanic pumice that preceded Mazama s collapse. As the surface of the hot pumice cooled over the years, steam and gases were released by the hot rocks underneath through vents and tubes that were welded into cement hardness by their passage. These ancient vents now stand alone due to the erosion of the surrounding softer materials.

16. Phantom Ship–A rugged island rising dramatically 175 feet above the lake surface, the “ship” is a remnant of an ancient volcano predating Mount Mazama, making this the oldest lava exposed in the caldera.

17. Sun Notch–This cross-section of a glacially scarred trough is located on the caldera rim. (Kerr Notch and Munson Valley are also evidence of glaciers that draped Mazama’s long slopes, some extending as far as seventeen miles toward the valley.)

18. Godfrey Glen and Colonnades–With the Pinnacles, this area ranks as the most significant feature along park roads other than those along Rim Drive. It is composed of fossil fumaroles marking the site of hot gasses that rose through the glowing avalanches that once filled the canyon.

19. Union Peak–Its summit is an old cinder cone which grew on top of an old shield volcano.

20. Llao’s Hallway–This 125-foot-deep gorge was cut through pumice material by stream erosion. It is located on Whitehorse Creek, a tributary of Castle Creek and once contained a trail leading through narrow passages to numerous cavelike amphitheaters.