The Geology of Crater Lake National Park, Oregon
With a reconnaissance of the Cascade Range southward to Mount Shasta by Howell Williams
It may be helpful to the visiting geologist to mention the features of particular interest that he should see according to the length of time at his disposal. If his stay be brief, he should devote it chiefly to examination of the caldera walls, for nowhere can he gain a clearer picture of the internal structure of, a volcano. Most calderas of comparable size are so deeply eroded or so masked by vegetation that their structure is difficult to decipher, but here the precipitous walls are bare and rise 2000 feet above the lake, revealing with singular clarity the manner in which the volcano was built. The visitor with only a day to spare should either drive around the caldera on the Rim Road, or, preferably, take the morning boat trip which encircles the lake close to the base of the cliffs. Should he take the trip by boat, he will find it pleasant and instructive to devote the afternoon to an excursion on Wizard Island, where he may examine the cinder cone and rugged lava field at its foot, products of the final eruptions within the park. If, on the other hand, he chooses the drive along the Rim Road, he should allow sufficient time to climb both the Watchman and Mount Scott, in order to gain a clearer picture of the geological setting of Crater Lake.
The walls of the caldera are unquestionably the most important feature of the park from a geological point of view. Perhaps next in interest are the pumice and scoria-filled canyons in the southern part of the park. Fortunately the highway from the eastern entrance follows the rim of Sand Creek canyon and provides many unobstructed views of the fantastically eroded fragmental deposits and of the “fossil fumaroles” which occur among them. The highway from the southern entrance follows the rim of Annie Creek canyon and affords similar views. If time permits, it is well worth while to examine the canyon walls from top to bottom, either at Godfrey’s Glen near Annie Spring or at the Pinnacles on Sand Creek.
Both the caldera walls and the pumice-filled canyons can be seen in a single day, but several days may be profitably devoted to more detailed examination of each. The only official trail down the caldera wall leads to the boat landing on the south side of the lake. Unfortunately, the descent here reveals less of interest than almost any other part of the entire circumference. In fact there is little of particular interest on the south wall of the caldera that cannot be seen adequately from a boat. But the north wall, from the Watchman to Redcloud Cliff, displays a wide variety of volcanic and glacial features deserving close inspection. Here may be seen the feeders of the dacite flows of Llao Rock, Cleetwood Cove, and Redcloud Cliff, and abundant dikes, including the Devil’s Backbone. For those interested in seeing moraines and fluvioglacial deposits interbedded with lavas, there are no better places than beneath the Roundtop and Palisade flows and along the southern side of Cloudcap Bay. Almost all the features just mentioned may be examined without difficulty or danger; some, however, are accessible only to one with a stout pair of climbing shoes and a steady head.
Next to an exploration of the walls of the pumice-filled canyons, perhaps the most interesting trip outside the caldera is to the summit of the Union Peak volcano. A motor road leads across the flanks of the glaciated lava shield to the base of the tuff cone inside the central crater and to the plug which fills the central conduit. Other trips may be made to the parasitic cinder cones on the slopes of Mount Mazama, though these show little that cannot be seen to better advantage on Wizard Island.