Abstract

Mapping of Quaternary sedimentary rocks and Miocene basalts on Toppenish Ridge, a fold in south-central Washington, reveals a 32-km-long zone of nearly 100 surface ruptures. The ruptures indicate renewed movement on Miocene structures in latest Quaternary time. The ruptures probably formed in response to regional compressive stress, between 500 and 13,000 yr ago. These ruptures are interpreted to represent the most recent surface deformation in central Washington.

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