Consisting of massive to poorly bedded shale, mudstone, and siltstone, it weathers readily to a rounded hilly topography with clayey, loamy soils in which landslides and slumps are frequent.

Outcrops of the unit are infrequent, with the best exposures on the coastal bluffs near Naples, in the San Marcos Foothills, at the Tajiguas Landfill, and in road cuts.

The geologic unit is notorious as a source of radon gas related to its high uranium content, released by radioactive decay.

At the ground surface, the contact with the Vaqueros is obvious along the south slope of the mountains, for it is almost always defined by the line dividing the rounded, grassy foothills from the more rugged, chaparral-covered sandstones upslope.

[5] The Rincon Formation is massive to poorly bedded, and consists of predominantly argillaceous to silty shale and mudstone, with occasional dolomite.

[3] As is common with shale units, the formation has a low permeability, and therefore where oil and gas reservoirs occur in the area it serves as the impermeable cap keeping the hydrocarbons in place.

[15] In Ventura County, the exposure of the formation along Los Sauces Creek has yielded ten different species of ostracoda; a detailed study suggested that the sea bottom they inhabited was around 2,000 meters deep, very near to the edge of the continental shelf.

[20] Some of the mitigation measures employed in houses on the Rincon Formation since the discovery of the problem in the 1990s include building ventilation systems for the air space beneath the structure, performing "soil suction" in which the gas is pulled directly from the soil under the building, and active house pressurization, which keeps the gas from entering.