FOREST GEOGRAPHY AND ARCHZOLOGY. 209 
coast there is no summer rain at all, except in the northern 
portion, and there little. And the winter rain, of forty-four 
inches on the northern border, diminishes to less than one 
half before reaching the Bay of San Francisco; dwindles to 
twelve, ten, and eight inches on the southern coast, and to 
four inches before we reach the United States boundary be- 
low San Diego. 
Taking the whole year together, and confining ourselves 
to the coast, the average rainfall for the year, from Puget 
Sound to the border of California, is from eighty inches at 
the north to seventy at the south, %. e., seventy on the 
northern edge of California; thence it diminishes rapidly to 
thirty-six, twenty (about San Francisco), twelve, and at San 
Diego to eight inches. 
The two rainiest regions of the United States are the Pa- 
cific coast north of latitude forty-five, and the northeastern 
coast and borders of the Gulf of Mexico. But when one is 
rainy the other is comparatively rainless. For while this Pa- 
cific rainy region has only from twelve to two inches of its 
rain in the summer months, Florida, out of its forty to sixty, 
has twenty to twenty-six in summer, and only six to ten in the 
winter months. 
Again, the diminution of rainfall, as we proceed inland 
from the Atlantic and Gulf shores, is gradual; the expanse 
that is or was forest-clad is very broad, and we wonder only 
that it did not extend farther west than it does. 
On the other side of the continent, at the north, the district 
so favored with winter rain is but a narrow strip, between the 
ocean and the Cascade Mountains. East of the latter, the 
amount abruptly declines, — for the year, from eighty inches 
to sixteen ; for the winter months, from forty-four and forty 
to eight and four inches; for the summer months, from 
twelve and four to two and one. 
So we can understand why the Cascade Mountains abruptly 
separate dense and tall forest on the west from treelessness 
on the east. We may conjecture, also, why this north Pa- 
cific forest is so magnificent in its development. 
Equally, in the rapid decrease of rainfall southward, in its 
