DOMINANT PRECIPITATION POINT. 15 



region of the Columbia River in Washington, and the animal rainfall is 

 barely sufficient to permit a moderate growth of tin? yellow pine and 

 1 )ouglas spruee there. Proceeding eastward from Spokane in the direc- 

 tion of the North Fork basin, a rapid increase in the density and size 

 of the forest growth soon becomes noticeable. The white fir, the west- 

 ern tamarack, the white pine, and the cedar appear, all of them species 

 requiring plenty of moisture for their development. Finding these 

 trees on the same level and under the same soil conditions as exist at 

 Spokane, avc are forced to the conclusion that a greater amount of pre- 

 cipitation takes place where they grow than is the case at the former 

 place, where they are absent. No other explanation for their distribu- 

 tion seems possible. Taking now T the annual precipitation for Spokane 

 as a basis, and considering the increase in the forest growth between 

 that point and the one at the western base of the North Fork rim of 

 mountains, an addition of 50 per cent to the annual fall of moisture is 

 very far within the bounds of probability. This would give 135 cm. 

 (about 53 inches) for a point about L'O kilometers (13 miles) east-north- 

 east from Rathdrum, Idaho. The water draining from the adjoining 

 ridges is excluded as a factor in the forest growth, for our station is 

 chosen in a locality where no water flows on the surface and where no 

 subwater is known to exist within 60 meters (about 200 feet) of the 

 same. Proceeding easterly from the station, we encounter the mountain 

 ridges, and the annual precipitation increases at a rapid rate as altitude 

 is gained. 



The winds that bring the moisture come from between the south and 

 southwest. For some unexplained reason the exact point between 

 these two directions from which the storms conn; varies slightly from 

 year to year, but is pretty uniform for each year. It. might be named 

 the dominant precipitation point. The degree of inclination which 

 this assumes each year in relation to the principal storm lines, the 

 south and southwest, appears to decide the animal amount of precip- 

 itation. The nearer to the south the warmer and moist er will be the 

 winter; the nearer to a westerly direction the colder and dryer will be 

 the season. Bat little attention has been given to this feature which 

 I have called the dominant precipitation point, but that it exists is 

 evidenced both by observations of the people living in the region and 

 by certain conditions of the forests, which will be explained farther on. 

 The latter class of records extends over at least two centuries. The 

 circumstance noted here is of very great importance in relation to 

 the conservation of the Cceur d'Alene forests, as we shall see pres- 

 ently. Many of the winter storms appear to come trom the north. In 

 reality this is only seemingly so. It is but the lower stratum of air 

 which travels southward in these cases. Whenever we obtain glimpses 

 of the moving cloud masses through the snow or rain during these 

 storms we see that at elevations above 1,800 meters (5,900 feet) or there- 

 abouts they come steadily from a southerly direction, no matter from 



