Coldwater Sandstone

Coldwater Sandstone Stratigraphic range: Middle and Upper Eocene
Coldwater Sandstone, Santa Ynez Mountains, north of Santa Barbara, California
Type	sedimentary
Underlies	Sespe Formation
Overlies	Cozy Dell Shale
Thickness	0 to 3200 feet
Lithology
Primary	sandstone
Other	siltstone, mudstone, occasional conglomerates
Location
Region	Southern California
Country	United States
Type section
Named for	Coldwater Canyon, tributary of the Sespe River, north of Fillmore
Named by	Watts(1896)

The Coldwater Sandstone (or Coldwater Formation) is a sedimentary geologic unit of Eocene age found in Southern California, primarily in and south of the Santa Ynez Mountains of Santa Barbara County, and east into Ventura County. It consists primarily of massive arkosic sandstone with some siltstone and shale. Being exceptionally resistant to erosion, outcrops of the Coldwater form some of the most dramatic terrain on the south slope of the Santa Ynez Mountains, with immense white sculpted slabs forming peaks, hogback ridges, and sheer cliff faces.

The type locality for the Coldwater Sandstone is in Coldwater Canyon, a western branch of the Sespe River a few miles north of Fillmore. The unit is typically around half a mile thick, ranging from 2,500 to 3,200 feet through most of its extent, although it thins westward to around 1,000 feet thick in the hills north of El Capitan State Beach. From there going west to Gaviota, the unit gradually grades into the Sacate Formation, a similar but shalier and more siltstone-rich unit which is also conformably overlain on the Cozy Dell Formation. The Coldwater and Sacate Formations are sometimes considered as a single unit, particularly underneath the Santa Barbara Channel where they appear in drill cores. The Gaviota Formation is deposited conformably on top of the Coldwater-Sacate in the western part of the dual unit's extent, and the Sespe Formation appears conformably on top of it elsewhere.

The Coldwater outcrops predominantly on the south slope of the Santa Ynez Range, and on the crest of the range at San Marcos Pass. Cathedral Peak, the 3,333-foot prominence directly north of Santa Barbara, is within the Coldwater unit. Because the sandstone beds are resistant to erosion, wherever they dip steeply, they form distinctive hogback ridges and dip-slopes, a topography particularly characteristic of the ridge north of Goleta, where the Coldwater accounts for almost all of the terrain above approximately 1,000 feet. While the unit is exposed prominently throughout the Santa Ynez Mountains, it dips steeply to the south and vanishes underneath the coastal plain and then the Santa Barbara Channel. Well bores in the numerous oil and gas fields in the Channel show the Gaviota Formation overlying the Cozy Dell directly, with no intervening Coldwater, excepting the offshore portion of the Capitan Oil Field, in which the Coldwater Formation is present as a natural-gas-bearing unit, underlying the Gaviota.