ruptions
diminished greatly in intensity.... Along the first summit of the
range west of Tahoe the greatest number of vents are found. Beginning
at Webber Lake on the north, they include Mount Lola, Castle Peak,
Mount Lincoln, Tinker Knob, Mount Mildred and Twin Peak. The andesite
masses here in places attain a thickness of 2000 feet. An interval
followed in the northern part of the Pyramid Peak quadrangle where no
important volcanoes were located, but they appear again in full force
in Alpine County. Round Top, attaining an elevation of 10,430 feet,
and the adjacent peaks, were the sources of the enormous flows which
covered a large part of Eldorado County. Still another volcanic
complex with many eruptive vents is that situated in the western part
of Alpine County, near Markleeville, which culminates in Highland Peak
and Raymond Peak, the former almost reaching 11,000 feet. The total
thickness of the volcanic flows in this locality is as much as 4000
feet."

It is to these breccias we owe the volcanic appearances in the Truckee
River Canyon, a few miles before reaching the Lake. There are several
layers of the andesites breccias at the head of Bear Creek Canyon,
above Deer Park Springs.

"None of the craters," says Lindgren, "of these volcanoes are
preserved, and at the time of their greatest activity they may have
reached a height of several thousand feet above the present summits."

CHAPTER VIII

THE GLACIAL HISTORY OF LAKE TAHOE

We have already seen in the preceding chapter how the great basin,
in which Lake Tahoe rests, was turned out in the rough from Nature's
workshop. It must now be smoothed down, its angularities removed, its
sharpest features eliminated, and soft and fertile banks prepared upon
which trees, shrubs, plants and flowers might spring forth to give
beauty to an otherwise naked and barren scene.

It is almost impossible for one to picture the Tahoe basin at this
time. There may have been water in it, or there may not. All the
great mountain peaks, most of them, perhaps, much higher by several
thousands of feet than at present, were rude, rough, jagged masses,
fresh from the factory of God. There was not a tree, not a shrub, not
a flower, not a blade of grass. No bird sang its cheering song, or
delighted the eye with its gorgeous plumage; not even a frog croaked,
a cicada rattled, or a serpent hissed. All was barren desolation,
fearful silence and ghastly newness.

What were the f