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 Formation
• 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
• Formations

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 basins.