Formation of the Pinnacles: Cracks and Deep Leaching


Step 3: The layer of Calcrete or caliche is breached by cracks and plant roots, allowing the rain water to preferentially dissolve the calcite in specific zones. These areas became enriched in quartz sand as the calcite was removed. Later (in step 4) when the plants die and the sand is blown away, these zones of leaching will tend to form the low spots between the more resistant pinnacles with the calcrete caps.

However other effects are sometimes well developed and preserved in the rocks. The line between cementation and dissolution is a fine one, controlled by details of chemistry, water availability and mineralogy. Zones on a scale of millimeters to centimeters around plant roots are commonly strongly cemented. When surrounded by less well cemented sand, these 'rhizoliths' (or fossil roots) commonly litter the surface of the Pinnacles Desert after the sand has been blown away. In other cases, clusters of roots can effectively cement towers of sand that look like pinnacles.

 Step 1

 Step 2

 Step 3

 Step 4