Field Trip To Ione Basin--October 22, 2002

Western Foothills Of The Sierra Nevada

Amador County, California

Another view of the dramatic, striking geologic contact in the Middle Eocene Ione Formation, seen in the previous image--here, brilliant white, massive fluvial (river-deposited) sandstones (mined for their commercial grade content of silica elsewhere in the Ione Basin) underlie thinly bedded reddish-brown shales and sandtones that contain a higher percentage of biotite and feldspar than the white sandstones below. Such a shift in mineral content demonstrates that the reddish-brown shales accumulated under paleoconditions that were less humid and rainy than the white sandstones. Dark-greenish brushes at base of the exposure are the rare and protected Ione manzanita, Arctostaphylos myrtifolia, which grows in the wild nowhere else on Earth, except on the acidic mineralized soils weathered from the Ione Formation in the Ione Basin, western foothills of the Sierra Nevada, Amador County, California. Image snapped on October 22, 2002.

Please note: All fossil localities in the Ione Formation of Amador County, California, presently occur on private property; explicit permission from the land owners must be secured before collecting fossils there.

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