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Chilcotin Ranges and Fraser Plateau

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About the Chilcotin Ranges and Fraser Plateau

The Chilcotin Ranges and Fraser Plateau constitute a region in interior British Columbia between the taller and more rugged mountain ranges along the coast and the Rockies to the east.

Most of this region is towards the cold, dry end of a humid continental climate; the climate becomes subarctic in the north and at the highest elevations, and semiarid in the southeast at the lowest elevations. The climate here is influenced by rain shadow from the coastal mountains. Throughout most of this region, precipitation is seasonal, following a different pattern from areas closer to the coast, with a dry season from late winter into spring, and wetter summers persisting somewhat into fall. However, the higher-elevation, more northerly parts of this region transition to having a climate more like that of the coastal mountains, in which there are wet winters and drier summers, although in this region the dry season peaks slightly earlier and precipitation picks up earlier as well, typically in September. Elevations decrease towards the southeast, particularly falling off towards Fraser and Chilcotin rivers, and the climate is driest and warmest there.

The terrain here formed as a plateau that was disrupted by recent glaciation, peaking about 15,000 years ago, in which the glaciers receded and melted abruptly, completely melting by about 13,000 years ago. The drainage patterns here thus reflect a pattern of outwash channels that are much larger than the rivers that currently fill them, and the areas between these channels are flat and have minimal dissection, with a dirupted drainage network marked by numerous wetlands and lakes. In the flatter areas, the landscape is marked with glacial features including moraines, compound eskers, glacial lake deposits, and depressions which are filled with lakes in places, and mucky organic soils in others. Descending to the rivers there are steep cliffs in places, and gentle slopes in others.

Soils here are mostly either the relatively richer, more-developed gray luvisols or the relatively poorly-developed dystric brunisols; these soils are acidic. A few of the warmer, lower-elevation sites in the major valleys also have chemozerms, or black soils, which are highly fertile soils rich in organic matter and with a high moisture-holding capacity, more amenable to agriculture.

Most of this region is forested, with closed forests of white spruce, lodgepole pine, quaking aspen, and Douglas fir. Slightly warmer, drier sites feature more open growth of lodgepole pine and Douglas fir. The highest elevations also feature Engelmann spruce and alpine fir. The lowest elevations along the Fraser and Chilcotin rivers feature grasslands dominated by bunchgrass.

In the northwest of this region, the hydrology has been altered by the Kenney Dam, which formed the Nechako Reservoir. This damming combined numerous small rivers and lakes in the northwest of this region into one large reservoir, and also diverted it to drain west into the Pacific ocean, where it had previously drained east into the Fraser river. This reservoir is sometimes called Ootsa Lake Reservoir, referencing the largest of the original lakes that became part of the reservoir. This project has created numerous ongoing environmental problems.