| Juncal Formation | |
|---|---|
| Stratigraphic range: Eocene | |
 Outcrop of the Juncal Formation, in the Santa Ynez Mountains, California. Shale with interbeds of sandstone (the lighter-colored material). | |
| Type | sedimentary |
| Underlies | Matilija Sandstone |
| Overlies | Sierra Blanca Limestone, Jalama Formation, Espada Formation, Franciscan Formation[1] |
| Thickness | 1,500 to 5,400 feet[2] |
| Lithology | |
| Primary | shale, sandstone |
| Location | |
| Region | Coastal southern California |
| Country | United States |
| Type section | |
| Named for | Juncal Camp, east of Agua Caliente Creek, Santa Barbara County |
| Named by | Page, Marks and Walker (1951)[3] |
The Juncal Formation (also Juncal Shale) (/ˈdʒʊŋkɑːl, ˈhuːŋ/) is a prominent sedimentary geologic unit of Eocene age found in and north of the Santa Ynez Mountain range in southern and central Santa Barbara County and central Ventura County, California. An enormously thick series of sediments deposited over millions of years in environments ranging from nearshore to deep water, it makes up much of the crest of the Santa Ynez range north of Montecito, as well as portions of the San Rafael Mountains in the interior of the county. Its softer shales weather to saddles and swales, supporting a dense growth of brush, and its sandstones form prominent outcrops.[4]