Nearly 7 miles of Los Angeles-area coastline was closed to beachgoers Thursday as scientists investigated mysterious balls of tar washing ashore.

Officials said it appeared to be about a barrel or two of oil -- nothing like the pipeline spill that created a 10-square-mile slick off the Santa Barbara County coast last week and killed some 16 birds and nine marine mammals.

Beaches from the El Segundo jetty south to Redondo Beach were off-limits to residents and visitors as crews cleaned up the mess that began accumulating on the sand Wednesday.

Public health officials told people to avoid contact with the water, wet sand or any material that washed up in the area. They warned that contact with petroleum products can cause skin irritation and result in long-term health problems.

There has been no indication so far of harm to wildlife.

The cause of the goo was a mystery. There's a refinery and offshore oil tanker terminal nearby, but the U.S. Coast Guard did not find a sheen from a spill. It could be residue from the Santa Barbara spill.

Also natural seepage has been known to leave tar balls on the sand -- and beachgoers' feet.