The Coast Guard says an oil slick that formed in the Pacific Ocean last week near Santa Barbara, California, was created by natural, ocean-floor seepage.

Tests conducted on samples from the thin layer of oil found its composition matched naturally occurring sources.

The slick was found Wednesday in the Santa Barbara Channel above the Coal Oil Point seep field, an area known for releasing methane and about 100 barrels of liquid petroleum a day.

The Coast Guard said Monday the slick was approximately 3 square miles. It wasn't thick and gooey enough to be scooped up and was expected to dissipate naturally.

The slick was located about 12 miles away from the site where an onshore pipeline ruptured in May, releasing up to 101,000 gallons of crude and fouling beaches.