There are signs posted all along a 2-mile stretch of beach 55 miles south of San Francisco that caution: "WARNING! Elephant Seal Bulls Are Dangerous!"

This is the only known place on earth where elephant seals -- huge 14-to 16-foot marine mammals weighing as much as 3 tons -- come ashore near a populated area to breed, give birth and molt.

Once nearly extinct, the seals have made a dramatic comeback on islands off the California coast and began coming ashore here 14 years ago. Experts believe they may move ashore on more beaches in the future.

But for now, the only way to see them is to take the guided 2 1/2-hour, 3-mile walking tours conducted here daily by park rangers and biology majors from the University of California, Santa Cruz. The State Parks Department has set up rigid controls to keep anyone from getting too close, but does allow groups within 20 feet of the basking seals.

Elephant seal bulls mate with as many females as possible, so the mobile bulls are constantly battling with one another for dominance among the females. Their clashes in the surf and on the sand, in which they slash one another with large canine teeth and inflict severe wounds, are among the bloodiest battles of any animal species. At times the fights are fatal.

While the violent courtship battles ensue, females group together on the sand. They bear their young -- after a gestation of one year -- within six days of coming ashore and then nurse the pups on the beach for a month.

Mating begins 24 days after the females give birth and after about a week the females leave in groups. The pups remain on the beach for a month or two before they, too, begin their swim.

There are two species of elephant seals. The southern species -- an estimated 300,000 -- thrives between Antarctica and the southern tip of South America. The northern species comes ashore for short periods each year on four Mexican islands off the coast of Baja California; on San Miguel, San Nicolas and Santa Barbara Islands off the coast of Southern California; on tiny Ano Nuevo Island off the Ano Nuevo State Reserve; in the Farallon Islands off San Francisco, and now on the mainland.

During the first half of the 19th century the giant seals were slaughtered for their oil. By the 1880s the northern was believed extinct. But a few years later scientists discovered a small herd numbering less than 50 on Guadalupe Island off Baja California.

"The northern elephant seal species made one of the most fantastic comebacks of any animal in history," says Burney Le Boeuf, 44, professor of biology at UC Santa Cruz and a leading authority on the huge marine mammal. Le Boeuf estimates the population of northern elephant seals at 60,000 and growing rapidly, all descendants of the Guadalupe Island seals of a century ago.

The first elephant seals were seen on 13-acre Ano Nuevo Island, a half-mile off Ano Nuevo State Reserve, in 1955. The first elephant seal pup was born on the island in 1961. Last year 872 pups were born on Ano Nuevo Island.

Elephant seals first made a landfall on the mainland across from Ano Nuevo Island in 1965. A single pup was born on the mainland in 1975. The following year seven pups were born on the mainland; in 1977 there were 16 elephant seal pups born on the beach here, and last year there were 86.

Le Boeuf has studied elephant seals at rookeries in North and South America. He and a number of assistants, including his wife, Joanne Reiter, also an expert on the marine mammal, have sprayed more than 12,000 of the big beasts with names and numbers for identification during the past dozen years.

"It will be interesting to see what will happen to the population explosion of sea elephants as time goes on," Le Boeuf said. "Where do they go from here? Elephant seals could get very political in the next few years if they continue to make inroads along the California coast."

Last year on San Miguel Island off Santa Barbara, 5,000 elephant seal pups were born. Nearly 1,000 pups were born on San Nicolas Island off the coast south of Ventura and about 100 pups were born on Santa Barbara Island west of the Palos Verdes Peninsula.