before present) to 17.5 - covering, with the Vaqueros Formation, the entirety of the lower Miocene.

The Rincon Formation weathers to a distinctive loamy, black soil with a high expansion-contraction potential, presenting a risk to structures built on soils derived from the formation. Landslides and slumps are frequent on soils produced from the Rincon, although they usually are not large, limited to about 15 feet in depth.

As is common with shale units, the formation has a low permeability, and therefore where oil and gas reservoirs

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