Sibley rock display: basaltic breccia from top of a flow

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Sibley's rock collection: basaltic breccia from top of flow

Basaltic breccia from top of a flow:
red color from steam action on hot fragments

This rock is displayed in “Sibley's Geological Treasures” collection on the roofed patio of the visitor center in the Robert Sibley Volcanic Regional Preserve. The above caption is the same that is given on-site (June 11, 2012).

Basaltic breccia is a rock composed of fragments of basalt and other rocks cemented together.

Breccias are found in the Berkeley Hills including the preserve's Round Top, which was once the infilling of a crater.