Wallace Creek, often bone dry for most of the year, preserves clear evidence of movement along the San Andreas fault, which crosses the ground there from northwest to southeast. The creek once flowed straight across the fault without bends, but repeated motion caused by large earthquakes every few hundred years gradually shifted the upstream half of the channel to the right of the downstream half. The creek’s two sharp bends and irregular shape show that the ground has moved there in the past and warn that earthquakes will occur there again in the future.