In general, geographers consider Lassen Peak as marking approximately the southern end of the Cascade Range, and as being the last of that series of great volcanic cones of which Rainier, Adams, Hood, Three Sisters, Mazama, Pit and Shasta are familiar examples. To the southeast of Lassen the topographic gap of the Feather River separates the Cascade Range from its correlative, the Sierra Nevada, which extends four hundred miles farther to Tehachapi Pass, but whose lofty peaks owe their height primarily to uplift rather than to volcanic upbuilding.
The southern fifty miles of the Cascade Range extending northwesterly toward Shasta from the North Fork of the Feather River is a great volcanic ridge, about twenty-five miles wide. This ridge is studded with numerous minor volcanic cones culminating in Lassen, the dominating peak, which is guarded by a number of other major cones rising to heights varying from seven thousand to nine thousand feet above the sea. Past volcanic phenomena of the Lassen Peak region in recent geologic time have been made familiar to readers through J. S. Diller’s well-known report,[1] which describes with considerable detail the Cinder Cone, ten miles northeasterly from the main peak, from the base of which the latest lava flow issued. Until the present outbreak, despite our knowledge of the Cinder Cone lava flows, it has been tacitly assumed in physiographic literature that Lassen Peak belonged to the class of extinct volcanoes, although the following statement by Diller in the folio just quoted shows clearly that twenty years ago he did not consider the volcano entirely extinct.
The latest volcanic eruption in the Lassen Peak district, and possibly the latest in the United States south of Alaska, occured at the Cinder Cone about two hundred years ago. Some of the trees killed at the time are still standing. The lava, although very viscous, spread more than a mile from the vent and formed a huge tabular pile which extends across a little valley. The lava dam thus formed developed Snag Lake, which contained stumps of some of the trees drowned at the time the lake originated.
That volcanic activity is not yet extinct in the Lassen Peak district is shown by the presence of numerous solfataras and hot springs. At Bumpass’s Hell, near the southern base of the peak, there are boiling mud pools and vigorous, solfataric action. Near by, at the head of Mill Creek, the sulphur deposited by such action is so abundant that attempts have been made to mine it. Similar phenomena occur in Hot Springs Valley and at Lake Tartarus and the Geyser, near Willow Lake. The Geyser is much less vigorous than formerly, and now the column of water rises scarcely a foot above its pool.
Previous to the present activity of Lassen Peak there had been numerous indefinite reports of eruptions witnessed by the Indians in that vicinity shortly before the coming of the white settlers. The most definite of these reports is given in a recent letter from Dr. J. W. Hudson, of Ukiah, California.
- ↑ Lassen Peak Folio, U. S. Geol. Survey, 1894.
