Every one familiar with
Arizona and New Mexico knows how the sudden summer showers fill the
mountain valleys with floods which flow down upon the plain and rapidly
spread out into broad, thin sheets, often known as playas. There the
water stands a short time and then either sinks into the ground or
evaporates. Such places are favored with the best kind of natural
irrigation, and after the first shower it is an easy matter for the
primitive farmer to go out and drop grains of corn into holes punched
with a stick. Thereafter he can count on other showers to water his
field while the corn sprouts and grows to maturity. All that he needs
to do is to watch the field to protect it from the rare depredations
of wild animals. As time goes on the primitive farmer realizes the
advantage of leading the water to particularly favorable spots and thus
begins to develop a system of artificial irrigation. In regions where
such advantageous conditions prevail, the people who live permanently
in one place succeed best, for the work that they do one year helps them
the next. They are not greatly troubled by weeds, for, though grasses
grow as well as corn in the places where the water spreads out, the
grasses take the form of little clumps which can easily be pulled up.
In the drier parts of the area of summer rain, it becomes necessary to
conserve the water supply to the utmost. The Hopi consider sandy fields
the best, for the loose sand on top acts as a natural blanket to prevent
evaporation from the underlying layers. Sometimes in dry seasons the
Hopi use extraordinary methods to help their seeds to sprout. For
instance, they place a seed in a ball of saturated mud which they
bury beneath several inches of sand. As the sand prevents evaporation,
practically all the water is retained for the use of the seed, which
thereupon sprouts and grows some inches by the time the first summer
floods arrive.

The Indians of the Great Plains lived a very different life from that
of the natives of either the mountains or the Pacific coast. In the far
north, to be sure, the rigorous climate caused all the Indians to live
practically alike, whether in the Rockies, the plains, or the Laurentian
highland. South of them, in that great central expanse stretching from
the latitude of Lake Winnipeg to the Rio Grande River, the Indians
of the plains possessed a relatively uniform type of life peculiar to
themselves. This individuality was due partly to the lux