When running water eddies, abrasive sand and small rocks swirl around with the water and wear a circular hole into the granite. Rocks trapped in the holes are also eroded, becoming rounded in shape. The holes are called "drill holes" and the rocks are "grinding cobbles". Examples can be found along Bald Rock Creek, at Underground Creek and along The Junction track.
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Abrasion Chutes.
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Drill hole with grinding cobbles, Bald Rock Creek, near The Junction.
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