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Boundary CountyBoundary County lies at the north end of the Idaho panhandle, and borders Canada. The western portion of the county is part of the Priest River uplift, exposing Cretaceous granitic rocks of the Kaniksu batholith, that intrude Mesoproterozoic Belt Supergroup, and overlying Neoproterozoic Deer Trail and Windermere groups and Cambrian rocks. A small Jurassic or Cretaceous granodiorite intrudes the Deer Trail Group in the northwestern part of the county. This intrusive is associated with accretion of rocks in British Columbia known as the Kootenay arc, a possible island-arc terrane. The eastern portion of the county, east of the east-dipping normal fault that bounds the Priest River core complex uplift, contains Belt Supergroup with small Cretaceous intrusions. A west-dipping thrust fault runs northwest-southeast, through Eastport, and formed during Cretaceous crustal shortening. Bonners Ferry, Eastport, and most of the habitable ground is found on the flat valley of the Kootenai and Moyie rivers, which flow north into Canada before joining the Columbia, whose course bends south and returns to the USA in eastern Washington. A glacial lake, dammed by piedmont ice to the north, occupied this long-north-trending valley, and so fine-grained lake beds underlie much of the Kootenai Valley. P.K. Link, 9/02 Additional ReadingRocks Rails and Trails: page References on Idaho Geology |
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Click here to see a correlation of geologic units, and the associated time scale. Click here for a printable version of this map.
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