r the Gila--the other but a diminutive stream,
scarcely reaching that river. At the head-waters of the Concho,
therefore, begins that great desert region, which, with no
interruption save a limited valley or bottom-land along the Rio
Grande, and lesser ones near the small courses mentioned, extends
over a district embracing sixteen degrees of longitude, or about a
thousand miles, and is wholly unfit for agriculture. It is a
desolate, barren waste, which can never be rendered useful for man or
beast, save for a public highway."--_Bartlett's Personal Narrative_,
vol. i. p. 138.

Turning now to Central and Upper California, and Utah, and Southern
Oregon, we find still another peculiarity. Like Southern Mexico, they have
a rainy and dry season, but at a different period, and for a different
reason. The dry season of California, etc., is the summer of the northern
hemisphere, and her rainy season the winter. _California_ is, therefore,
_dry_ when Southern _Mexico_ is _wet_, and _vice versa_. The belt of rains
which supplies California with moisture during her rainy seasons is the
belt of _extra-tropical_ rains, which extends from the northern limit of
the north-east trades to the poles, encircling the earth. The southern
edge of this extra-tropical belt is _carried up_ on the western coast of
America, and in that portion of the continent in _summer_, when the sun
and trades, and the inter-tropical rainy belt travel to the north, and
uncover California, etc., leaving them without rain for a period of about
six months.

[Illustration: Fig. 3. IN SUMMER.]

As the sun, with the trades, travels south, the southern edge of the belt
of extra-tropical rain follows, and covers California, etc., again
extending gradually from the north to the south, and thus their wet
season returns. The annexed diagrams by the shading will show the
situation of the rainy belts which cover Mexico, Utah, New Mexico, and
California in summer and winter, and that the belts of rains are entirely
distinct and different in character.

[Illustration: Fig. 4. IN WINTER.]

Here again in this section of the continent, as in Mexico, evaporation is
going on for six months of the year, and were it not for the return of the
belt of rains from the north, in the fall, would go on for the entire year
without precipitation; and for the other six months precipitation is
vastly in excess. Nor can this be reconcile