J. LeConte—Extinct Volcanoes about Lake Mono. 85 
Art. IV.—On the Extinct Volcanoes about Lake Mono, and their 
relation to the Glacial Drift; by JosepH LeConte. 
[Read before the National Academy of Sciences, April 16, 1879.] 
In 1870, and again in 1872, in company with a party of stu- 
dents and graduates of the University of California, I visited 
the Mono region. But on both occasions my attention being 
specially directed to the study of the ancient glaciers, I exam- 
ined the volcanoes only somewhat cursorily. In 1875 with a 
similar party I again visited the same region, and this time 
remained longer and examined more carefully, though on ac- 
count of an unfortunate accident, not so long or so carefully as 
I desired. I have put off from year to year the publication of 
the results of my observations in the hope of again visiting the 
region and settling some doubtful points which still remained. 
There seems now, however, little likelihood that I shall ever 
be able to carry out my intention, for other questions of still 
greater interest have in the meantime engaged my attention. 
I will therefore no longer withhold my imperfect observations, 
hoping that they will be corrected and extended by others. 
General description of the region.— Eastern slope of the Sierra. 
—As already explained in previous papers,* the general form 
of the Sierra is that of a great wave ready to break on its east- 
ern side. It rises from the San Joaquin plains by a gentle 
slope which extends 50 to 60 miles, reaches a crest 13,000 feet 
high, then plunges downward by a slope so steep that it reaches 
the plains of Mono 6000 ft. above sea level, in five or six miles. 
In glacial times, long, complicated glaciers with many tributa- 
ries occupied the western slope, while on the east, comparatively 
short simple glaciers came down in parallel streams and ran 
far out on the level plain and into the swollen waters of Lake 
Mono, which, then nearly 700 feet above its present level and 
far beyond its present limits, washed against the base of the 
Sierra itself. There can be no doubt that these glaciers formed 
icebergs which floated on the surface of the great inland sea 
and dropped débris over its bottom. 
The Plains.—Surrounding Lake Mono and sloping imper- 
ceptibly to its surface, is a nearly level desert plain, covered 
with volcanic sand interspersed with fragments of pumice and 
obsidian, and overgrown with sage-brush (Artemisia tridentata). 
It is undoubtedly an old lake bottom, subsequently covered 
with voleanic ashes. -The dreary prospect of this desert is re- 
lieved by the magnificent irregular Sierra wall trenched with 
deep cafions; by long parallel moraine ridges stretching like 
arms from the mouth of each cafion, five or six miles out on 
* This Journal, III, v, 326, 1873; x, 126, 1875; xvi, 95, 1878. 
