Large regions in which major late Cenozoic basin-range fault blocks are consistently tilted are recognized in the western United States. The pattern of tilt domains is characterized by transverse zones or boundaries, parallel to the extension direction, and by antiformal (tilts away from) and synformal (tilts toward) boundaries at right angles to the extension direction. Tilting of ranges averages about 15° to 20° in Nevada and Utah and indicates extension of about 20% to 30% for-the entire Great Basin region, using the model proposed by Morton and Black (1975) that relates dip of beds and extension. The regional tilt pattern may be related to stress relief extending outward from antiformal boundaries that are interpreted as initial sites of rupture during late Cenozoic extension.

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