Offshore Geology of Santa Barbara County
Santa Barbara Channel, Islands and Coastline
Approximately 100 million years ago, the area that is now Santa
Barbara County was part of the ocean floor. At the end of the Miocene
epoch (about 5 million years ago), plate movement along the San
Andreas Fault thrust the earth's crust skyward. This action created
the Santa Ynez Mountain Range and lowered the seafloor of what became
the Santa Barbara Channel. Approximately 3 million years ago, the
ancient island of Santarosae was lifted from the seafloor by similar
action. This island was part of an underwater mountain range that
parallels the coastline of Santa Barbara County.
Over time, plate movement along the San Andreas Fault caused the
Santa Barbara Channel, island of Santarosae, and the Santa Ynez
Mountains to become aligned east to west. This east to west alignment
was made easier because this area rests on an individually mobile
piece of the earth's crust located between the Pacific Plate and
North American Plate.
Approximately 12,000 years ago the last ice age came to an end.
Glaciers melted and sea levels rose. As a result, low-lying areas
of Santarosae were flooded creating the separate islands of San
Miguel, Santa Rosa, Santa Cruz, and Anacapa.
Two geologic basins lie off Santa Barbara County's coastline. One
of these basins is the Santa Maria Basin. The southern offshore
extremity of this basin is located approximately off the coast of
Point Conception. The Santa Maria Basin is about 150 miles long,
10 to 50 miles wide, and is approximately 3,000 square miles in
size. The other geologic basin is the Santa Barbara-Ventura Basin.
This basin abuts the Santa Maria Basin at its northwestern extremity
near Point Conception and proceeds east-southeast into neighboring
Ventura County. The Santa Barbara-Ventura Basin is about 185 miles
long, up to 55 miles wide, and approximately 5,000 square miles
in size. Both of these basins include onshore and offshore reserves.
Many different geologic plays exist within the two basins discussed
above. Within these plays exist various rock formations. Some of
these formations contain oil and gas reservoirs. Within the Santa
Maria Basin, the following formations are noted as maintaining oil
or gas reservoirs:
- Miocene Monterey
- Miocene to Pliocene Sisquoc and Pismo Formations
- Lower to middle Miocene Point Sal Formation
- Lower Miocene Lospe Formation
- Sisquoc, Santa Margarita, and Foxen Formations
The primary components of the rock strata that comprise the oil
or gas reservoirs in this basin consist of fractured chert, porcelanite,
dolomite, or various sandstones.
Within the Santa Barbara-Ventura Basin, the following formations
are noted as maintaining oil or gas reservoirs:
- Non-marine Eocene to early Miocene Sespe Formation
- Shallow marine Vaqueros Formation
- Eocene Matilija, Coldwater Sandstone, and Llajas Formations
- Paleocene clastic rocks
- Pliocene and Pleistocene Pico Formation
- Miocene and lower Pliocene Rincon, Monterey, Modelo, Sisquoc,
and Santa Margarita
The primary components of the rock strata that comprise these oil
or gas reservoirs consist of various fractured sandstones and fine-grained
silicious rocks. The following stratigraphic columns illustrate
the underlying rock layers of the Santa Maria and Santa Barbara-Ventura