Juncal Formation

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
Thickness	1,500 to 5,400 feet
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)

The Juncal Formation (also Juncal Shale) (/ˈdʒʊŋkɑːl/ or /ˈhuːŋkɑːl/) 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.

The type locality of the Juncal Formation is found north of the Santa Ynez River and east of Agua Caliente Canyon, near Juncal Campground in the Los Padres National Forest, where the unit is well-exposed. At the type locality the Juncal Formation is 3,360 feet thick, which is about average; elsewhere it is both thicker and thinner, reaching 5,400 feet thick near the Romero Saddle north of Carpinteria, and thinning to 1,500 feet north of the Santa Ynez Fault in Oso and Redrock Canyons.