Cozy Dell Shale

Cozy Dell Shale Stratigraphic range: Eocene
Talus slope on an outcrop of Cozy Dell Shale, Santa Ynez Mountains, California.
Type	sedimentary
Underlies	Coldwater Sandstone
Overlies	Matilija Sandstone
Thickness	350 to 4,000 feet (107 to 1,219 m)
Lithology
Primary	shale
Other	minor sandstone beds, calcareous nodules
Location
Region	Coastal southern California
Country	United States
Type section
Named for	Cozy Dell Canyon, Ventura County
Named by	Kerr and Schenck (1928)

The Cozy Dell Shale is a geologic formation of middle Eocene age that crops out in the Santa Ynez Mountains and Topatopa Mountains of California, extending from north of Fillmore in Ventura County westward to near Point Arguello, north of Santa Barbara. Because the Cozy Dell easily weathers to a clay-rich soil, it crops out infrequently and generally forms dense stands of chaparral in saddles between peaks and ridges of the more resistant Matilija and Coldwater formations.

The Cozy Dell was first described in 1928 as the middle member of the Tejon Formation. However, Dibblee (1966) reclassified it as a formation, along with the underlying Matilija Sandstone and overlying Coldwater Sandstone. He also named the formation after its type locality at Cozy Dell Canyon, which is located on the south side of Nordhoff Ridge, just north of Ojai in Ventura County.

The Cozy Dell crops out continuously in the mountains to the north and east of Ojai, where it is exposed along much of the south slope of the Topatopa Mountains in Ventura County, and continues westward along the south slope of Santa Ynez Mountains into Santa Barbara County. Here, it is overlain by younger rocks at San Marcos Pass, on the crest of the Santa Ynez Range, cropping out west of the pass and forming much of the crest north of Goleta. It disappears north of the Santa Ynez Mountains beneath younger formations, and is removed, for the most part, by erosion north of the Santa Ynez River, where it appears at only a few localities. It grades into and is overlain by the Sacate Formation in the western part of its outcrop belt, and dips south beneath the modern California coastal plain in the southern part. Continuing south into the offshore region beneath the Santa Barbara Channel, the Cozy Dell is found in oil wells at Molino field some 13,000 feet (3,962 m) feet below the sea floor.