NOTES ON THE DOUGLAS FIR. 1 9 



ranges to the western skirts of the Cariboo and Monashee 

 Mountains. It varies from 140 to 170 miles in width, and is 

 traversed by the Fraser River and its tributaries and by some 

 of the tributaries of the Columbia River. The valleys of the 

 main rivers and the larger tributaries have the same trough- 

 shape as the great intermontane valleys, and bear evidence of 

 having been scoured by valley glaciers except in the upland 

 portions, where the outlines are V-shaped, and of the type 

 associated with ordinary stream erosion. The rainfall averages 

 about 15 inches but in some places is less than 10 inches. 

 Owing to the small rainfall, conditions that are almost semi-arid 

 prevail throughout the larger part of the plateau. On the up- 

 lands, as is shown by the records obtained at the meteorological 

 stations, the rainfall is heavier than in the valleys. Extremes 

 of temperature are experienced, the summers being warmer and 

 the winters much more severe than in the Coastal Belt. In the 

 southern part of the plateau the mean annual temperature is 

 about 45°, with a winter mean of 25° and a summer mean of 65°. 

 The extremes vary from - 45° to over 100°. 



The town of Kamloops is near the junction of the North 

 Thomson and Thomson Rivers, the latter one of the chief tribu- 

 taries of the Fraser River. On the bottom lands in this region 

 at altitudes of 700-1000 feet above sea-level the land is a sage- 

 brush {Artemisia tridentata) desert, which merges into a grass- 

 land {Agropyriim spicattini) on the lower slopes, the latter in turn 

 giving place at altitudes of 1500-2500 feet to an open forest of 

 western yellow pine {Pitius ponderosa). The Douglas fir, which 

 is frequently present as an understory to the western yellow pine, 

 forms an almost pure forest in the middle altitudinal zone above 

 2500 feet, and in turn, at higher elevations and on more exposed 

 sites, is replaced by Engelmann's spruce and lodgepole pine. 



The yellow pine is confined to the more southern portions of 

 the Interior Plateau, where the forests, owing to their accessi- 

 bility and the quality of the yellow pine timber, have been 

 heavily exploited, but outside of this region the lumbering 

 industry is of little importance. The Douglas fir in the Interior 

 Plateau rarely attains a height greater than 70-80 feet, and the 

 quantity of timber to the acre usually averages less than 1000 

 cubic feet. 



The Kamloops cones, which were gathered in the middle 

 altitudinal zone, where the Douglas fir forms practically pure 



