FOREST TREES OF THE PACIFIC SLOPE. 103 



Colusa County: Northwest corner on Snow Mountain. Lake Comity: East side of 

 Coast Range to Long Valley, Upper Cache Creek, Clear Lake, and to point near Middleton. 

 Common in Del Norte, Humboldt, Mendocino, Marin, and Sonoma counties (coast ranges) ; 

 abundant westward to eastern margin of redwood belt, and sparingly through it, some- 

 times to the sea. Del Norte County: Westward to Crescent City. Humboldt County: 

 Sparingly among the redwoods north of Humboldt Bay ; westward south of bay to Fern- 

 dale and Hear River valleys, ivtrolia. Upper Ifattole River, Briceland, and south slope of 

 Kini.' Mountain. Mendocino County: Westward to Kenny, Westport, Mendocino Pine 

 Barrens, mouth of Big River, and seaward gulches from Fort Bragg to Gualala. Sonoma 

 County: Westward in north part to east edge of lodgepole pine belt (on coast) to 

 point 1 mile from beach at Fort Ross, near mouth of Russian River, nearly to Bodega 

 Bay, Meeker, and Occidental. Marin County: Westward to southern part of Inverness 

 Ridge (Point Reyes Peninsula), line of North Shore Railroad, and valleys of San Ger- 

 onimo and Lagunitas. Napa County: Mount St. Helena, up to 4,350 feet, and south- 

 ward on ridge east of Napa Valley at least to St. Helena ttowni, and on ridge west side 

 of Napa Valley to point south of and to a point little beyond Oakville. Mountains about 

 San Francisco Bay; but not in Vaca Mountains (inner Coast Range). Oakland Hills, and 

 Mount Hamilton, nor Monte Diablo ranges. Frequent in Santa Cruz and Santa Lucia 

 Mountains, at 2,500 to 3,000 feet, southward to Los Burros. Throughout Santa Cruz 

 Mountains from hills south of San Francisco and southward around north part of Mon- 

 terey Bay to within a few miles of Watsonville, reappearing southward in Santa Lucia 

 Mountains. 



The detailed range of Douglas fir in Idaho. Montana, South Dakota. Colorado, 

 Utah, Texas, New Mexico, Arizona, and Mexico will be dealt with in a later 

 bulletin. 



OCCURRENCE. 



Except at high elevations and at north limit, prefers north to south exposures and 

 sheltered slopes, canyons, benches, etc., to exposed situations. In north, and at high 

 elevations, warmer south exposures are preferred, as heat, not moisture, becomes the con- 

 trolling factor. Lower limit in drier regions determined by lack of moisture, and upper 

 limit chiefly by lack of heat. At higher levels on east sides of ranges than on west sides, 

 also higher on south slopes than on north exposures; but it is more abundant on west 

 singes than on east slopes, and likewise more frequent on north than on south exposures — 

 except at north, where heat is the controlling factor. Adapted to a great variety of soils, 

 including nearly all with sufficient moisture, from border of brackish coast water to soils 

 where only drought-enduring western yellow pine grows. Prefers fresh, well-drained, 

 porous, deep, loamy soils, avoiding saturated, poorly drained, heavy soils. Good soil and 

 abundant atmospheric and soil moisture are necessary for best growth, but with abundant 

 moisture, quantity and quality of soil are less important, and vice versa. Grows faster 

 and larger on poor gravels and sand in the humid Tuget Sound country than on best soils 

 of Rocky Mountains with dry air and deficient precipitation ; likewise, not so large on best 

 soils of drier California mountains, even though the climate is mild and heat and sunshine 

 are abundant for tree growth. 



Forms large pure forests and often nearly pure stands, but chiefly associated with 

 numerous species of different habits. In California Sierras chiefly with yellow pine, 

 sugar pine, white fir, and incense cedar, as also in Cascades of southern Oregon ; while in 

 California coast ranges it grows with redwood and tanbark oak. In Oregon and Wash- 

 ington, mainly with western hemlock, western red cedar, lowland fir, western yellow pine, 

 and on coast, with Sitka spruce, while in coast ranges and in Cascades it occurs with 

 western white pine, western larch, and lodgepole pine. 



Climatic Conditions. — Climate varies from moist one of Northwest to dry one in 

 parts of interior and Southwest, and from the short growing season of high elevations 

 to the long growing season of warm, humid coast region, and of the sunny Southwest. 

 Winter varies from rainy season, as in parts of Pacific coast region, and an occasional 

 snow storm and short cold snap followed by summer's heat, as in the southern Rocky 

 Mountains, to more severe winter of the Rockies northward to interior British Columbia : 

 in northern Idaho and Montana winters are lon^ and temperature drops frequently 

 as low as —30° or —40° F. Average annual precipitation and relative humidity, extremely 

 variable. Precipitation varies from over 100 inches (Puget Sound) to less than 15 

 inches (dry interior and Rockies). Amount of precipitation diminishes from coast to 

 Rockies and from British Columbia to New Mexico: it increases with elevation and is 

 less on east than on west side of coast ranges. Cascades, Sierras, and Rockies. Relative 

 humidity of air is high where precipitation is great. To sum up. this tree grows best 

 in greatest abundance where precipitation and relative humidity of the air are greatest. 



