{{Short description|Eocene Epoch geologic formation in California}} {{Infobox rockunit | name = Ione Formation | image = Hematitic kaolinite (Ione Formation, Middle Eocene; clay pit in the western foothills of the Sierra Nevada Mountains, central California, USA).jpg | caption = A rock from the Ione Formation | type = Geologic formation | age = Eocene | period = Eocene | prilithology = | otherlithology = | namedfor = | namedby = | region = California | country = United States | coordinates = | unitof = | subunits = | underlies = Chico Formation (regionally) | overlies = Martinez Formation (regionally) | thickness = | extent = | area = | map = | map_caption = }}
The '''Ione Formation''' is an Eocene Epoch geologic formation in California.<ref>{{Cite web |title=Science |url=https://www.science.org/action/cookieAbsent |access-date=2026-02-07 |website=AAAS |language=en |doi=10.1126/science.40.1019.67}}</ref><ref>{{Cite web |title=Type Region of the Ione Formation (Eocene), Central California: Stratigraphy, Paleogeography, and Relation to Auriferous Gravels |url=https://pubs.usgs.gov/of/2006/1378/ |access-date=2026-02-07 |website=pubs.usgs.gov}}</ref><ref>{{Cite web |title=Geolex — Ione publications |url=https://ngmdb.usgs.gov/Geolex/UnitRefs/IoneRefs_5647.html |access-date=2026-02-07 |website=ngmdb.usgs.gov}}</ref>
==Geology== The formation regionally overlies the Martinez Formation and regionally underlies the Chico Formation.
=== History === The auriferous gravels accumulated on slope of Sierra Nevada during the Neocene Period, and at same time there was deposited in the gulf then occupying the Great Valley a sedimentary series consisting of clays and sands.
=== Description === It is usually overlain by a few feet of reddish Pleistocene gravel and rests on Chico formation. The strata form flat-topped hills, and consists of a succession of light-colored clays and white or yellowish-white sandstones. The largest development occurs south of American River.
==See also== {{Portal|California|Paleontology}} * List of fossiliferous stratigraphic units in California * {{C|Paleogene California}} * Paleontology in California
== References == {{Reflist}}
Category:Geologic formations of California Category:Eocene Series of North America Category:Geology of Contra Costa County, California Category:Geology of Los Angeles County, California Category:Geology of Orange County, California Category:Geology of Riverside County, California Category:Natural history of the Santa Monica Mountains