of the Sierra Nevada and Cascade ranges.
They are remarkable both for the number of species and for the
size of the trees. The moderate temperature and the moist winds
from the Pacific seem to offer the conditions which are best suited
to the growth of cone-bearing trees.

As we go northward along the coast, or ascend the mountain slopes,
we find the climate growing cooler and cooler. With this changing
climate the species of conifers change, for each has become accustomed
to certain conditions of temperature and moisture, which it must
have in order to thrive.

The Sierra Nevada is the most continuous lofty range of mountains
in North America. From the great valley at its western base to the
crest of the range the distance is about sixty miles. Because of
the great height of the mountains, there is found within these few
miles every variety of climate between the sub-tropical atmosphere
of the valley, where oranges ripen to perfection, and the arctic
cold of the summits, where little or no vegetation can live.

Thus, by climbing a single mountain range, we may experience all
kinds of climate, and have an opportunity to observe the different
forms of plant life such as we could not otherwise obtain without
a journey of several thousand miles.

[Illustration: FIG. 122.--FOREST BELT OF THE FOOT-HILLS, SIERRA
NEVADA MOUNTAINS]

Passing through the groves of valley oak, and beyond the orange
orchards at the foot of the mountains, we reach the foot-hills
and begin to ascend. Several species of oak are found upon the
hillsides and in the valleys, while mingled with them in many places
appear such shrubs as the California lilac, chamiso, and manzanita.
Where the soil is too poor or the slopes too steep for the trees,
these shrubs, commonly called "chaparral," are massed together
in almost impenetrable thickets.

The first of the coniferous trees which we meet is an odd-looking
one known as the digger pine. Instead of having a single straight
trunk it divides a short distance above the ground into many branches.
The large cones are armed with long hooked spines, so that they
must be handled rather carefully, but when opened they are found
to be filled with nutritious nuts. These nuts were an important
source of food for the Indians who once inhabited the foot-hills.
Now the Indians are gone, but the nuts are not wasted, if one may
judge by the fragments of the cones with which the squirrels strew
the ground.

[Illust