The bulk of Kootenai County south and east of Coeur d'Alene is underlain by Mesoproterozoic Belt Supergroup rocks continuing west from their extensively mineralized area along the Lewis and Clark fault zone, in the Silver Valley in Shoshone County.
The western part of the county, west of Coeur d'Alene Lake and the Rathdrum Prairie belongs to the lower plate of the Priest River core complex. The normal fault bounding the uplifted metamorphic rocks of the core complex dips eastward and follows the north-trending basin of Lake Coeur d'Alene.
The south fork of the Coeur d'Alene River contains mining wastes from the Silver Valley. The area near Rose and Killarney Lakes as well as at Cataldo, contains a layer of zinc and lead-rich gravel or tailings, in the shallow subsurface. When the lake level changes these mine wastes are disturbed and metals may be released into solution. This is an ongoing scientific, political, and economic challenge.
The Lake Missoula Floods charged southwestward down the Rathdrum Prairie toward Post Falls, and into the Spokane River in eastern Washington.
Miocene Columbia River basalts cover the rolling Palouse country of the southwestern part of the County, north of the Coeur d'Alene Tribal Casino.
Cretaceous intrusive rocks are found in the core of the Priest River uplift south of Coeur d'Alene, and northeast of Hayden Lake. Eocene granitic rocks intrude the core complex west of Spirit Lake.
Written by P.K. Link, 9/02
Rocks Rails and Trails: page
References on Idaho Geology
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