Cordilleran metamorphic core complexes consist of granitic cores surrounded by, in an outward direction, mylonite, chloritic breccia, and microbreccia. These rocks are separated by a low-angle detachment fault from typically unmetamorphosed but normally faulted rocks. Rocks above the detachment fault have been transported, relative to the core rocks, in one consistent direction, giving a distinct lineation to rocks below the detachment fault.

Dome-shaped metamorphic core-complex mountains show considerable structural control of landforms. Mylonitic rocks develop triangular dome facets around the margins and low relief areas in the central parts of the complexes. Chloritic breccia is much less resistant to erosion and has been almost completely removed from many complexes.

Drainage patterns in metamorphic core complexes are mainly radial, but an older set of drainage lines parallel to mylonitic lineation, especially channels that drain down the crests of antiformal ridges, suggests that drainage developed on a ramp on the detachment fault and the underlying breccia prior to lineation-parallel arching.

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