formed of silting while they still constituted beds
of lakes, have a deep soil of fine sand and mold resting on
coarse gravel and bowlder drift. Ridges composed of brecciated
lavas, which crumble easily under the influence of atmospheric
agencies, are covered with soil two or three feet, or even
more, in depth, where gentle slopes or broad saddles have
favored deposition and prevented washing. The granite areas of
the main range and elsewhere have a very thin soil. The flats
at the entrance of small streams into Lake Tahoe are covered
with deep soil, owing to deposition of vegetable matter
brought from the slopes adjacent to their channels. As a
whole, the soil of the region is of sufficient fertility to
support a heavy forest growth, its depth depends wholly on
local circumstances
favoring washing and removal of the soil elements as fast
as formed, or holding them in place and compelling
accumulations.[1]

Coniferous species of trees constitute fully ninety-five per cent.
of the arborescent growth in the region. The remaining five per
cent. consists mostly of different species of oak, ash, maple,
mountain-mahogany, aspen, cottonwood, California buckeye, western
red-bud, arborescent willows, alders, etc.

Of the conifers the species are as follows: yellow pine, _pinus
ponderosa_; Jeffrey pine, _pinus jeffreyi_; sugar pine, _pinus
lambertiana_; lodge-pole pine, _pinus murrayana_; white pine, _pinus
monticola_; digger pine, _pinus sabiniana_; white-bark pine, _pinus
albicaulis_; red fir, _pseudotsuga taxifolia_; white fir, _abies
concolor_; Shasta fir, _abies magnifica_; patton hemlock or alpine
spruce, _tsuga pattoniana_; incense cedar, _libocedrus decurrens_;
western juniper, _juniperus occidentalis_; yew, _taxus brevifolia_.

[Footnote 1: John B. Leiberg, in _Forest Conditions in the Northern
Sierra Nevada_.]

The range and chief characteristic of these trees, generally speaking,
are as follows:

_Digger Pine_. This is seldom found in the Tahoe region, except
in the lower reaches of the canyons on the west side of the range. It
is sometimes known as the Nut Pine, for it bears a nut of which the
natives are very fond. It has two cone forms, one in which the spurs
point straight down, the other in which they are more or less curved
at the tip. They grow to a height of forty to fifty and occasionally
ninety feet high; with open crown and thin gray fo