NATURAL AREAS AND REGIONS 



181 



3. OREGON' 



By Thornton T. Munger, William E. 



Lawrence and Howard M. 



Wight 



I. general CONDITIONS (t. T. M.) 



1. Topography 



The state borders on the Pacific 

 Ocean, it is traversed by coast ranges of 

 mountains near the ocean, and by a much 

 higher range, the Cascade Range, far- 

 ther inland, between which is a trough- 

 like series of valleys of low altitude and 

 less humidity than the westward slopes of 

 each range. East of the Cascade Range 

 is a plateau of arid or semi-arid condition 

 intersected by deep canyons on which are 

 scattered detached mountain masses. 

 The altitudes in Oregon range from sea 

 level on the west to 11,253 ft. on Mt. 

 Hood. The prevailing altitude of most 

 of eastern Oregon is over 3500 ft. 



The ocean strip has salt marshes, and 

 sand dunes; the interior has every type 

 of flood plain, valley floor, ravine, can- 

 yon, swamp, hillside and bluff; the high 

 mountains have talus slopes, old and 

 fresh moraines, alpine meadows and 

 wastes, mountain meadows or bogs, re- 

 cent and old lava flows, waterfalls, 

 natural lakes and uncontaminated 

 streams; and the Eastern Oregon plateau 

 has deserts, alkali and fresh lakes and 

 swamps, and mountains and valleys of 

 every description. 



Soils. There is a wide range in soils 

 over the state. Pure sand on the dunes 

 of the Coast and Columbia River, great 

 areas of loess in eastern Oregon, glacial 

 deposits in the mountains, river de- 

 posits, peats, and of special interest, 

 great areas of fresh volcanic ash and 

 pumice which blanket parts of the 

 Cascade Range and eastern Oregon, to- 

 gether with lava flows upon which soil 

 formation has hardly started. 



2. Climate 



Precipitation. West of the Coast 

 Range and on the western slopes of the 



1 Where there was no cooperation between the 

 authors their names stand in the order of the receipt 

 of their manuseripts and the authorship of the 

 different parts is indicated. 



Cascades the annual precipitation is 

 over 100 in. The valleys between the 

 Coast and Cascade Ranges have about 40 

 in. per year, well distributed except dur- 

 ing a two months' summer drought. 

 East of the Cascade Range the climate is 

 dry, ranging as low as 7 in. and averaging 

 perhaps 20 in. 



Temperature. West of the Cascade 

 Range the climate is very equable, ex- 

 treme heat and cold being rare. The 

 diurnal range is small. It is an insular 

 climate. Along the ocean strip a mini- 

 mum winter temperature as cold as 20°F. 

 is uncommon. East of the Cascade 

 Range the climate is continental and 

 extremes of both heat and cold are ex- 

 perienced. Cold nights (frosts at the 

 higher altitudes) are the rule throughout 

 the year. Much cloudy weather is 

 usual west of the Cascades while clear 

 skies and considerable wind are the rule 

 east of the mountains. On the moun- 

 tains an alpine climate prevails. 



3. Original biota 



A. Plant^ communties {W. E. L.). A 

 summary of the plant associations of 

 western Oregon follows: 



Douglas fir forest (Hygrophytic conif- 

 erous forest) 



Spruce forest (Hygrophytic coniferous 

 forest) 



Cedar-hemlock forest (Hygrophytic 

 coniferous forest) 



Redwood forest 



Siskiyou chaparral 



Hill prairie (or grassland) 



Valley prairie (or grassland) 



The Cascade Range of Mountains ex- 

 tending from the California line to the 

 Columbia river, divides the state of Ore- 

 gon into an eastern dry and a western 

 humid section. This long mountain 

 range serves as an effective barrier to the 

 moisture laden winds from the ocean. 

 The natural flora of the two sections, 

 therefore, differs in the principal species 

 of plants and the landscape aspect. 



Westerii Oregon. Western Oregon is 

 characterized by a moister climate due to 

 the Cascade barrier. The Coast Range 



- Scientific names of plant.s mentioned in British 

 Columbia and Washington do not occur here. 



