Thousands of elephant seals are returning to Año Nuevo State Park, where construction is finishing on spiffy new facilities

It’s one of Northern California’s most famous wildlife shows.

Every year, up to 10,000 elephant seals — the giant, blubbery pinnipeds that can weigh 5,000 pounds, grow as long as a Toyota Corolla and hold their breath underwater for 2 hours — haul out of the ocean at Año Nuevo State Park along the San Mateo County coast to breed, give birth, fight, harrumph and generally carry on.

Nearly 100,000 people from all over the world join guided tours at the park between Dec. 15 and March...