Jalama Formation

Jalama Formation Stratigraphic range: Cretaceous
Dark shale beds of the Jalama Formation on the Santa Ynez Mountain crest north of Montecito, California. These beds are overturned; "up" is down and to the left.
Type	Sedimentary
Underlies	Juncal Formation, Sierra Blanca Limestone
Overlies	Espada Formation, Franciscan Formation
Thickness	2000-4000 feet
Lithology
Primary	Shale, sandstone
Location
Region	Coastal and interior Santa Barbara County, California
Country	United States
Type section
Named for	Jalama Creek
Named by	Dibblee (1950)

The Jalama Formation is a sedimentary rock formation widespread in southern Santa Barbara County and northern Ventura County, southern California. Of the Late Cretaceous epoch, the unit consists predominantly of clay shale with some beds of sandstone.

A particularly erosion-resistant sandstone within the unit forms the scenic Nojoqui Falls, in the Santa Ynez Mountains south of Solvang.

The type locality of the Jalama Formation is in southwestern Santa Barbara County on the low ridgeline between Santa Anita and Bulito Canyons, within Hollister Ranch, near the crest of the Santa Ynez Mountains, and near the headwaters of Jalama Creek. The formation is found from this area eastward along the Santa Ynez Range in periodic outcrops, underlying either the Anita Shale (in the western portion of its range) or the Juncal Formation Shale (in the east). The largest outcrop in the Santa Ynez Range is along the north slope of the mountains near Santa Ynez Peak, where it is exposed for approximately six miles. Other outcrops occur north of the Santa Ynez Fault, in the San Rafael Mountains along the Little Pine Syncline and along the Hildreth Fault.

Characteristic shale beds within the Jalama are dark gray to black, micaceous, and often carbonaceous. Sandstones interbedded with the shales are arkosic, light gray to tan, and sometimes massive, as at the base of the type section on Hollister Ranch. Another interbedded unit occasionally encountered is a cobbly conglomerate, which outcrops on the north slope of the Santa Ynez Mountains south of Gibraltar Reservoir. The cobbles in this unit are detritus from a granitic source rock in a gray to brown matrix. The overall Jalama Formation varies in thickness from around 2,000 feet near the Romero Saddle north of Carpinteria, to about 4,000 feet at the type location more than forty miles to the west.