Mid-creation, Hawaii's actively volcanic Big Island—as close as you can get to the Garden of Eden—is still sprouting shameless pleasures. Mike Di Paola reports on a ten-year plan to further heighten temptation.

The expanse of black rock, flanked by a highway, is one uninviting swath of landscape. As first impressions go, this one is bleak. It speaks of destruction on a grand scale—the aftermath of war, a lifeless planet, or Hell cooled off. But leave the main road, aim for the beach, and suddenly the harsh, dark beauty of a newborn shore with palm and cactus edging the coal-black lava is revealed.

Contradictions abound on the Big Island's Kona-Kohala coast, which has become Hawaii's Riviera of posh resorts. I begin my explorations on one of the last undeveloped beaches, Kekaha Kai, which has been a state park since 1995. On a weekend morning of off-and-on sunshine, I have it to myself. The arc of salt-and-pepper sand is bisected by a centuries-old lava flow—a legendary one. An old lady, the story goes, asked for a bite to eat from the local chief, who rebuffed her. A bad move. She was no ordinary crone but the goddess Pele herself, and she delivered vengeance in the form of molten rock from Hualalai, sparing only the one villager who fed her dinner.

On the Big Island, every piece of land comes with a story. Kekaha Kai Beach was once owned by a part-Hawaiian family, the Magoons, whose abandoned home still sits at the north end. They sold the land to a Japanese investor in the 1990s, but when development was prohibited, he sold the parcel to the state—a sweet deal for us, except that Hawaii's state parks are distressingly neglected.

The contrast between state-maintained and privately maintained beaches is stark on this coast. Very near Kekaha Kai State Park is a pristine gem, the site of Laurance Rockefeller's Mauna Kea Beach Hotel, which opened in 1965, the pioneer resort on the island, an instant classic, and a must-see.

The cul-de-sac that is the Mauna Kea's tiny public parking lot is already nearly full by 9:30 a.m., when I arrive. The water is warm and clear, so I dive in and, while bodysurfing the gentle waves, I observe the uncrowded beach. This splendid white crescent is bisected not by lava but by an invisible socioeconomic barrier: Hotel guests stay at one end, around the pool, and the hoi polloi are effectively segregated at the other, equally lovely end.

Then there's Hapuna Beach, my next stop. A half-mile sandy arcadia, Hapuna lies between Mauna Kea and Kekaha Kai and reflects elements of both. On one end is the massive, plush Hapuna Beach Prince Resort; on the other, Hapuna Beach State Recreation Area, with its open parking lot, family picnic tables, rudimentary concession stand, and public restrooms, which, as one guidebook noted, "look like they're from the Third World."

All that is about to change. This year, the state tourism authority will begin a ten-year plan to protect and enhance its parklands. The initiative is statewide, but splendid Hapuna Beach is one of its priorities, perhaps because this island—younger, less developed, and with a more definitive tinge of native defiance—might have the most riding on its success. How the state treats its own property is crucial here on the Big Island, which has more than two-thirds of Hawaii's landmass and is still growing, lava flow by lava flow.