Geologic Units |
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Miocene basalt (Columbia River Basalt Group) |
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Dioritic, gabbroic, granitic, and amphibolitic rocks of the Blue Mountains island arc terrane |
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Martin Bridge and Hurwal Formations (Wallowa Terrane) |
| Map Key | |
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Geologic units with unit designation. |
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Normal Fault: certain; dashed where approximately located; dotted where concealed. |
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Thrust Fault: certain; dashed where approximately located; dotted where concealed. |
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Detachment Fault: certain; dashed where approximately located; dotted where concealed. |
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Interstate Route. |
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U.S. Route. |
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State Route. |
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Location of Rockwalk rock from the county. |
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Cities. |
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Feature location. |
Lewis County
Lewis County, on the south side of the Clearwater River, contains the steep sided Camas Prairie plateau underlain by Miocene lava flows of the Columbia River basalts. Poking through at several places are Cretaceous and Jurassic island arc rocks of the Accreted terranes. The Suture zone runs just east of the county line along the Clearwater River through Kamiah.
These plateaus are unusual, since the flat ground is on top, and the cities are generally in narrow valley bottoms.
The Clearwater River cuts through the plateau, following the track of the Cretaceous suture zone.
Written by P.K. Link, 9/02
Additional Reading
Rocks Rails and Trails: page
References on Idaho Geology
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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