Page:Atlantis Arisen.djvu/86

74 high, rolling prairies, extending to the base of the Blue Mountains, which trend south westwardly, leaving plains and small valleys, to the east, between themselves and the Snake River, which forms the eastern boundary of Oregon and a portion of Washington.

These differences in altitude would of themselves produce differences in temperature. But the great reason why the change is so great from the coast to the Snake River lies in the arrangement of the mountain ranges, and in the fact that the northwest shore of the American continent is washed by a warm current from the Japan Sea. The effect of this current is such that places in the same latitude on the Atlantic and Pacific coasts are several degrees—sometimes twenty degrees—warmer on the latter coast than on the former. This gives a temperature at which great evaporation is carried on. The moisture thus charged upon the atmosphere by day is precipitated during the cooler hours of night in fog, mist, or rain.

In summer, the prevailing wind of the coast is from the northwest, thus following the general direction of the shoreline. It naturally carries the sea-vapor inland; but the first obstacle encountered by these masses of vapor is a range of mountains high enough to cause, by their altitude and consequent lower temperature, the precipitation of a large amount of moisture upon this seaward slope. Still, a considerable portion of moisture is carried over this first range and through the gaps in the mountains, and falls in rain or mist upon the level prairie country beyond. Not so, however, with the second, or Cascade Range. These mountains, by their height, intercept the sea-fog completely; and while great masses of vapor overhang their western slopes, on their eastern foot-hills and the rolling prairies beyond not a drop of dew has fallen. This is the explanation of the difference in climate, as regards dryness and moisture, between East and West Oregon. All other differences depend on altitude and local circumstances.

Notwithstanding the great amount of moisture precipitated upon the country west of the Cascades, the general climate may be said to be drier than on the Atlantic coast. The atmosphere does not seem to hold moisture, and even in rainy weather its drying qualities are remarkable. Taken altogether, the stormy