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Why do rivers in the California Coast Ranges often follow northwest-southeast fault lines?

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Pacific mountain system Coast Mountains along the Torres Channel, an arm of Atlin Lake, northwestern British Columbia, Canada.

In the California Coast Ranges, rivers often follow northwest-southeast fault lines because these faults represent significant lines of structural weakness within the region's geology.1

The California Coast Ranges are composed of folded and faulted sedimentary rocks. Unlike the ranges in Washington and Oregon, where the structural orientation is north-south, the major fault systems in the California Coast Ranges trend northwest-southeast. Because these fault lines create zones of fractured or less resistant rock, they provide a path of least resistance for water drainage, causing rivers to align with these tectonic features. Notable examples of rivers that follow these patterns include the Napa, Russian, and Eel rivers north of San Francisco Bay, as well as the Salinas River to the south.1