This rock is displayed in
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).
Sandstone is a sedimentary rock composed of quartz and feldspar grains. These sand-sized mineral grains are typically held within a silt or clay matrix.
Cretaceous sandstone formed during the Cretaceous period between 145 to 65 million years (Ma) ago. Its inclusion as xenolith in lava happened during times of volcanic activity; for example, about 10 Ma ago at Sibley's.