On bare open granite pavements, rock basins or "gnammas" form in depressions where rainwater collects. The submerged granite breaks down into clay and sand. When the tiny pools dry up, the wind blows the sand and clay away. Likewise, flood waters also clear out the basins. Because the weathering occurs in standing water, the sides of these pits tend to be vertical. There is a good collection of gnammas next to Bald Rock creek, not far from the Day-use area.
"Gnamma" is an Aboriginal word, originating from Western Australia where the local rock basins held an important water source for the indigenous people.
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Sandy Soils.
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A gnamma at Bald Rock Creek.
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