The eastern portion of the United States is supplied with abundant rainfall for agricultural purposes, receiving the necessary amount from the evaporation of the Atlantic Ocean and the Gulf of Mexico; but westward the amount of aqueous precipitation diminishes in a general way until at last a region is reached where the climate is so arid that agriculture is not successful without irrigation. This Arid Region begins about midway in the Great Plains and extends across the Rocky Mountains to the Pacific Ocean. But on the northwest coast there is a region of greater precipitation, embracing western Washington and Oregon and the northwest corner of California. The winds impinging on this region are freighted with moisture derived from the great Pacific currents; and where this water-laden atmosphere strikes the western coast in full force, the precipitation is excessive, reaching a maximum north of the Columbia River of 80 inches annually. But the rainfall rapidly decreases from the Pacific Ocean eastward to the summit of the Cascade Mountains. It will be convenient to designate this humid area as the Lower Columbia Region. Rain gauge records have not been made to such an extent as to enable us to define its eastern and southern boundaries, but as they are chiefly along high mountains, definite boundary lines are unimportant in the consideration of agricultural resources and the questions relating thereto. In like manner on the east the rain gauge records, though more full, do not give all the facts necessary to a thorough discussion of the subject; yet the records are such as to indicate approximately the boundary between the Arid Region, where irrigation is necessary to agriculture, and the Humid Region, where the lands receive enough moisture from the clouds for the maturing of crops. Experience teaches that it is not wise to depend upon rainfall where the amount is less than 20 inches annually, if this amount is somewhat evenly distributed throughout the year; but if the rainfall is unevenly distributed, so that “rainy seasons” are produced, the question whether agriculture is possible without irrigation depends upon the time of the “rainy season” and the amount of its rainfall. Any unequal distribution of rain through the year, though the inequality be so slight as not to produce “rainy seasons”, affects agriculture either favorably or unfavorably. If the spring and summer precipitation exceeds that of the fall and winter, a smaller amount of annual rain may be sufficient; but if the rainfall during the season of growing crops is less than the average of the same length of time during the remainder of the year, a greater amount of annual precipitation is necessary. In some localities in the western portion of the United States this unequal distribution of rainfall through the seasons affects agriculture favorably, and this is true immediately west of the northern portion of the line of 20 inches of rainfall,