Eocene

Eocene (1999), sited at the Paradise Ridge Sculpture Grove in Santa Rosa, CA, is a symbolic recreation of the climate of the Eocene geologic period of Northern California, which occurred from 40 to 60 million years go. Within a small region of moss covered rocks, live oak and laurel trees a moisture-laden microclimate has been created by a timed system of misting nozzles attached to the tree limbs emitting periodic rain showers on the area. The lushness of the misted area becomes more pronounced as the surrounding vegetation changes towards a golden brown during the summer months.

As the lower Eocene progressed the climate (of central California) became warmer and by the end of the lower Eocene had become subtropical. The Sierra Nevada had been worn down to a surface of low relief and was covered by a deep mantle of decomposed debris, the result of deep chemical weathering under hot humid conditions. (Taliaferro, 1951)

Pliocene

A companion work to Eocene, Pliocene considers a rock unit from the ‘Sonoma Volcanics’ of the Pliocene period in Northern California from 1 to 10 million years ago. The top section of a prominent volcanic rock in the grove is cut off in-situ to a level surface, ground smooth and polished. This incision reveals the inner structure and nature of the rock and the surrounding lava flow otherwise obscured by centuries of weathering.

‘Sonoma Volcanics’ is the name given to a thick accumulation of flows, agglomerates, tuffs and tuffaceous land-laid sediments that extend from the southern end of Sonoma Mountains, on the north side of San Pablo Bay, northwestward through Napa, Sonoma, and Lake Counties.

Their thickness depends on the nature of the surface over which they accumulated and the proximity to centers of eruption. In the bay counties their maximum thickness is about 1200 feet, but in places they are over 2000 feet thick.

In composition they have a wide range, including rhyolites, dacites, andesites, hypersthene andesites, basalts and olivine basalts. Some of the flows are very glassy and obsidians equivalent in composition to rhyolite, dacite and andesite are found. (Taliaferro, 1951)

John Roloff, 1999