Comparisons of the 2005 Geologic Map of North America with the 1965 Map, Areas 5-7
6. Cordillera of the northwestern United States and southwestern Canada
Like the view of the Caribbean, this view illustrates the importance of the seafloor geology in understanding the on-land geology.
- Refinements of the on-land geology include more detailed subdivision of the sedimentary rocks of the California Coast Ranges (A), the metamorphic and igneous rocks of the Klamath Mountains (B) and northwest Sierra Nevada (C), and the Tertiary volcanic rocks of the Columbia River (D) and Oregon Plateaus (E). Especially notable is the subdivision of rocks shown on the old map simply as "Cretaceous granitic intrusive" in the Sierra Nevada (C) and in northern Washington and southern British Columbia (F). On the new map they are subdivided into more than a dozen units based on age and lithology. In addition, dozens of faults including those in the San Andreas fault system, the Sierra Nevada, and the Basin and Range province have been added on the new map.
- The most important change is the addition of the seafloor geology, including portrayal of the Juan de Fuca (G) and Gorda (H) Ridges, the complex of thrust faults in the accretionary wedge (I) off Washington and Oregon and the array of normal and strike slip faults (J) in the California Borderland. These additions help illustrate the relations between the Gorda and Juan de Fuca spreading centers and recent and on-going volcanic activity in the Cascades, as well as the connection between spreading centers in the East Pacific Rise and Gulf of California (in parts of the map south of this view), the San Andreas fault system (K), and the Mendocino fracture zone (L).
Return to comparisons of map areas 5-7.
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