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<p>Unnamed fragile rock stack in Grass Valley area in the San Bernardino Mountains in California. The rocks lie near the San Andreas Fault within one of the highest seismic-hazard areas in the United States.</p>
<p>Courtesy of Lisa Grant Ludwig</p>

Precariously balanced rocks provide clues for unearthing underground fault connections

Stacked in gravity-defying arrangements in the western San Bernardino Mountains, near the San Andreas Fault, granite boulders that should have been toppled by earthquakes long ago resolutely remain. In exploring why these rocks still stand, researchers have uncovered connections between Southern California’s San Jacinto and San Andreas faults that could change how the region plans for future earthquakes.