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The Geology and Petrography of Crater Lake National Park


Twenty years ago Crater Lake was unknown to the general public, but since then a knowledge of its remarkable features has been spread abroad through the press, and Congress recognized its worth as an educational feature and made it a national park by the act approved May 22, 1902.

As defined in the bill, the park is "bounded north by the parallel forty-three degrees four minutes north latitude, south by forty-two degrees forty-eight minutes north latitude, east by the meridian one hundred and twenty-two degrees west longitude, and west by the meridian one hundred and twenty-two degrees sixteen minutes west longitude, having an area of two hundred and forty-nine square miles."

The Ashland sheet of United States Geological Survey, on the scale of 4 miles to 1 inch, includes the area lying between meridians 122° and 123° and parallels 42° and 43°. This map includes the region between Ashland and Crater Lake. On account of the great scientific interest of Crater Lake a special map, known as the Crater Lake special sheet, was prepared on the scale of 1 mile to an inch, including the country immediately adjacent to Crater Lake, between meridians 122° and 122° 15' and parallels 42° 50' and 43° 4'. From these two maps the accompanying map of the Crater Lake National Park (Pl. 1) has been prepared.

The two) papers published here refer practically to the whole region included in the National Park. The one, Part I, treats primarily of the geology, the development of the great volcano, Mount Mazama, and its collapse, which gave birth to) Crater Lake; the other, Part II, deals with the petrography, and gives a special description of the various rocks occurring in the park.

Origin of the name Mount Mazama.a—A great impetus to the spread of information concerning Crater Lake was given by the Mazamas of Portland, Oreg., who held a meeting at the lake in August, 1896, which attracted many visitors. The principal features in the history of the lake had previously been made out, and the Mazamas, recognizing the fact that the great peak which was nearly destroyed in preparing the pit for the lake had no name, gave it the name of their own society. Upon the rim of the lake are a number of small peaks, each having its own designation. The term Mount Mazama refers to the whole rim encircling the lake. It is but a mere remnant of the once lofty peak, the real Mount Mazama, which rose far into the region of eternal snow. To get a basis for reconstructing the original Mount Mazama it is necessary to study in detail the structure and composition of its foundation, now so attractively displayed in the encircling cliffs of Crater Lake.

aAn account of the discovery of Crater Lake and reference to its literature will be found in Mazama, vol. I, No. 2, Crater Lake number, 1897; National Geographic Magazine, Vol. VIII, p. 33, and the Annual Report of the Smithsonian Institution for 1897, p. 369.


Crater Lake is deeply set in the summit of the Cascade Range, about 65 miles north of the California line. It can be reached only by private conveyance over about 80 miles of mountain roads from Ashland or Medford, on the Southern Pacific Railroad, in the Rogue River Valley of southern Oregon (see fig. 1, p. 18), or from Ager, on the same railroad, in northern California, by way of Klamath Hot Springs and Klamath Falls.

Rogue River Valley marks the line between the Siskiyou Mountains of the Klamath group on the west and the Cascade Range on the east. The journey from the railroad to Crater Lake affords one a good opportunity to observe some of the most important features of this great pile of lavas. The Cascade Range in southern Oregon is a broad irregular platform, terminating rather abruptly in places, especially at the western border, where the underlying Cretaceous and Tertiary sediments come to the surface. It is surmounted by volcanic cones and streams of lava, which are generally smooth, but sometimes rough and rugged. The cones vary greatly in size and are distributed without regularity, a feature which is well illustrated in Pl. II. The photograph was taken across the western edge of Crater Lake. The sharp peak on the right is Union Peak and in the distance is Mount Pitt. Each conical hill has been an active volcano. The fragments blown out by violent eruption have fallen about the orifice from which they issued and built up cinder cones. From their bases have spread streams of lava (coulees), raising the general level of the country between the cones. At some vents many eruptions, both explosive and effusive, have built up large cones, like Pitt, Shasta, and Hood. Their internal structure is revealed by the walls of the canyons carved in their slopes, and they are found to be composed of overlapping layers of lava and volcanic conglomerate. This type of structure is well illustrated in the base of Mount Mazama.

The Dead Indian route from Ashland, Oreg.—The journey from Ashland by the Dead Indian road crosses the range where the average altitude is less than 5,000 feet, and affords a fair view of the low part of the range traversed by the Klamath River. A much better general view of the larger features of the range, and especially of the Crater Lake region, may be obtained front Mount Pitt (elevation 9,760 feet), which lies within a two days' trip from this road at Lake of the Woods. The road skirts Pelican Bay of Klamath Lake, famous for its fishing, and after running northward for about 20 miles along the eastern foot of the range it ascends the slope along the canyon of Anna Creek to the rim of Crater Lake.

The Klamath Falls route from Ager, Cal.—The approach from the east may be made also by a longer route, leaving the railroad at Ager, Cal., and traveling by stage road along the Klamath River, through the Cascade Range to Klamath Falls and Fort Klamath, from which point Crater Lake is only 20 miles distant by way of the Anna Creek road, already noted. The older tilted lavas of the Cascade Range dipping to the east are well exposed on this route at many points along the Klamath River road between Ager and Klamath Hot Spring.a Across the edges of these lavas, nearly 1,000 feet above the present river bed, is an ancient wide valley of the Klamath River, associated with gentle topographic relief at higher levels. Later lavas have crossed the range in this wide old valley and the Klamath River has cut a deep canyon in them. Within this young canyon, north of Bogus post-office, there has been a volcanic eruption, forming a dam across the Klamath and a consequent ponding of the river, in which a mass of white diatom earth was formed. The products of this eruption are much younger than any others known to the writer in the neighboring portion of the Cascade Range.

aThis celebrated health resort has a good hotel, fine scenery, hunting, and fishing.

The Rogue River route from Medford, Oreg.—From Medford the road by way of Rogue River, although 75 miles in length, is somewhat the shortest route. It affords some fine views of the canyons and rapids of that turbulent stream and of the high falls, where it receives its affluents, especially Mill Creek, below Prospect. A few miles below the mouth of Union Creek is a remarkable natural bridge of lava, but some distance from the main road. Striking features along the roads on both sides of the mountain, within 20 miles of the lake, are the plains developed upon a great mass of volcanic detritus filling the valleys. Across these plains Anna Creek and Rogue River have carved deep, narrow canyons with finely sculptured walls, which the roads follow for some distance.

The main road, whose grade is in general very gentle, crosses the summit 3 miles south of Crater Lake, and from the western slope near this point the crest of the rim is reached by a road with several heavy grades. There are good camping grounds with plenty of pasture on Castle Creek beyond the forks of the road and within 2-1/2 miles of the lake. At the end of the road, on the rim of Crater Lake, the camping places are fine, but pasture and water are not so abundant nor so easily obtained. There are as yet no hotels nor permanent accommodations for travelers at the lake, but during August and September, the most favorable months for visiting the lake, temporary accommodations should be provided and travel encouraged.


By far the most impressive and, to the geologist, most important trip about Crater Lake is by boat front Eagle Cove along the western and northern shore of the lake to Cleetwood Cove and Rugged Crest, returning by way of the crater capping the cinder cone in Wizard Island. It can be made in a day, but may require hard rowing. The rare opportunity of travelling about in the interior of a volcano could hardly be anything else than intensely interesting. The descent by the trail and cruise along the shore disclose the alternately overlapping sheets of andesitic lava and conglomerate of which the rim is composed. These are cut by dikes—a prominent one is at Devils Backbone, and smaller ones occur beneath Llao Rock. Some of these are andesite, but others dacite. The great flow of Llao Rock, over 1,200 feet thick in places and tapering to thin edges on the sides, is dacite. It is younger than the andesites of the rim and fills an old valley. At Pumice Point layers of pumice and streams of dacite overlie platy andesite which was glaciated before the dacites were erupted, and at Cleetwood Cove is seen the inflowing dacite from Rugged Crest and the caved-in lava tunnel to the northward. The latest flow of the rim is the tuffaceous dacite along the northeast crest from Pumice Point to the Wineglass, but later even than this is the excellent example of a little volcano which forms Wizard Island, with its cinder cone capped by a perfect crater summit, marking the vent from which the cinders were blown. From the island and the boat the glacial notches in the southern rim of the lake and the dacite flows of Cloud Cap and the eastern rim may be seen to greatest advantage.

The most instructive day's walk from the rim camp (Camp 1 on map), but a rather hard one, is along the western crest to Llao Rock. Glacial striae are best displayed along this portion of the rim. Andesites are exposed all the way to the Llao Rock flow, which near the edge may be examined both above and below. The inflow of Cleetwood Cove is clearly visible from a distance, and an excellent view of the crest of the Cascade Range may be obtained.

Those who may wish to make a camping trip around the lake are advised to take a pack train and devote a number of days to the trip, as the distance around the crest of the rim is over 20 miles and over much of the route traveling is difficult. There is no definite horse trail around the rim, but a practical pack route, with camping places indicated by numbers, is marked upon the map (Pl. I).

The canyon of Sun Creek is difficult to cross, as its western wall is precipitous. Near the notch there is pasture and good camping, but lower down, where the trail crosses, feed and water are scarce. At Camp 2, on the west fork of Sand Creek, there is plenty of both. Camp 3 has many attractions besides the fine firs and flowers. The great cliffs are inspiring, and the rustling of numerous little cascades gives a life to this inclosed camp that is not to be found elsewhere about the lake.

The ascent of the east side of Sand Creek Canyon is steep and somewhat difficult, but the fine views of the lake from the eastern rim in the morning abundantly pay for the special exertion necessary to attain them.

Camp 4 has some pasture and snow water. Beneath the large cliffs just north of the camp water was obtained for the animals. To the northeastward about 3 miles, in the line of the canyon heading at Cloud Cap, are fine springs and a cascade 50 feet in height. There is considerable pasture here, but on the whole the place is less inviting for camping than locations close to the crest. From this camp the descent to the lake may easily be made at the "wine-glass"-shaped slide of Grotto Cove.

At the head of Cleetwood Cove the crest is very rugged and somewhat difficult to cross with animals, but elsewhere travel along the northern rim of the lake is easy. Near the foot of Red Cone there is good camping by a spring. At many points along the lower slope of the western rim of the lake there are fine camps, plenty of grass, wood, and water, but in the past the sheep have greatly injured the pasture. Near the crest cliffs and rough talus slopes make traveling difficult and dangerous for animals. The easy and safe but longer route lies west of the cliffs to Camp 6, which is the main pasture camp of the region, with fine water.

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Last Updated: 07-Mar-2006