Andesite and balsite are medium
to dark-gray in color and can be seen as exposed bedrock, cliffs, and
boulders throughout the park.
An area of tuffaceous volcanic rock can be seen west of Upper Lake at the “Rock Garden.”
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| Rockville Park consists mainly of weathered bedrock from the Pliocene Age. It has a rugged outer area surrounding an elevated plateau, the Upper Bowl. The elevation of the park ranges from 100 feet at the park entrance to 565 feet above sea level on Green Valley Hill. | Notable higher elevations in the park are named Mystic Ridge which is southwest of Upper Lake and Manzanita Hill which is in the chaparral section of the park. | ||||||||||
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| The bedrock of the park was created 10 million years ago from volcanic activity northwest of Napa, Sonoma, and Lake counties. Known as the Sonoma Volcanics, the geologic formations of the park consist of andesiste and balsite flows interspersed in thick layers of tuff or volcanic ash. | Andesite and balsite are medium
to dark-gray in color and can be seen as exposed bedrock, cliffs, and
boulders throughout the park. An area of tuffaceous volcanic rock can be seen west of Upper Lake at the “Rock Garden.”
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