When four Alaskan grizzly bear cubs boarded a special FedEx plane last month bound for California, veterinarian Joel Parrott, armed with anesthetics, sat a few feet away from the very important cargo, and waited for something to go wrong.

Somehow, he said, “everything went right.”

Until that point, most things in the lives of the cubs — two sets of brothers — hadn’t been so. One of the moms wandered into a building in an oil rig town, the other into the city limits of Anchorage, Parrott said. Both were deemed threats to the public and “dispatched” — Alaska Department of Fish and Game lingo for “shot.”

For Parrott, president and CEO of the Oakland Zoo, the flight was a rescue mission. The cubs, orphaned and desensitized to human civilization, were considered “non-releasable” and slated for euthanasia.

“There are so many levels to talk about,” Parrott said. “You can talk about it at the species level — how do we live with wildlife? Then you can also talk about it in that very specific bear, that it was rescued from what was going to be a very sad ending. And if we can step into compassion and provide them a quality place to live, they can have a good 30-year life.”

The Oakland arrival of the four crates carrying the bears signified more than just snatching a few mammals from the jaws of death. It marked the penultimate stage of the zoo’s ambitious new exhibit after more than two decades in the making: the 56-acre California Trail, nestled in the East Bay hills with sweeping Bay Area vistas.

The project awaits a jaguar, a few bald eagles and some finishing touches, but it will be open to the public July 12. The Chronicle and other news media toured the exhibits Wednesday.

Now Playing:

The cubs were just the kind of animal that could find a home at the trail project, which more than doubles the zoo’s size to 100 acres, putting its footprint on par with the San Diego Zoo. Compared to the Southern California attraction, Oakland Zoo has far fewer animals, and Parrott said that’s intentional.

“We’re very sensitive to the fact that we don’t really want to have too many animals,” Parrott said, “because it allows us to have more space for the animals we have. When we come to visit, or we come to work here, and then we go home at night, the animals still have to stay and live here. So it’s incumbent upon us to make sure they have a high-quality life.”

The California Trail, designed to showcase the state’s biodiversity, has become a landing spot for a host of misfit creatures in recent months: parentless mountain lion youngsters that couldn’t survive in the wild, bears that got too close to humans, birds with broken beaks and so on.

“They aren’t here because of anything they did,” said Darren Minier, assistant director of care, conservation and research at the zoo. “It’s things we did as humans.”

Now Playing:

The zoo has no plans to breed the animals, with a few exceptions, Minier said. A male and female gray wolf, for instance, are expected to have a few litters to give them a natural pack structure. Their species has only recently resurfaced in California after nearly a century of statewide extinction.

It’s not the captive couple’s only tie to the broader state. The zoo is working with the California Department of Transportation so that when deer are hit and killed by cars, their carcasses can be frozen and delivered to the wolf enclosure as feed.

The $80 million California Trail, which carved out a slice of the city-owned Knowland Park, got permit approval in 1998 but was stalled by a number of challenges from preservation groups seeking to maintain the hillside.

Construction started three years ago. On top of building the enclosures, the project also involved weeding out invasive plant species and restoring native ones in and around the exhibits.

The animals — American buffalo, black bears, grizzly bears, brown bears, mountain lions, jaguars, California condors, gray wolves and bald eagles — were selected for their historic significance to the state.

“We want the people of the Bay Area to know about the amazing wildlife that exists, or existed, right here,” said Colleen Kinzley, Oakland Zoo’s director of animal care, conservation and research. “We still have this incredible wildlife. Do we want to allow them to stay and be part of our environment? Or do we want to see them go the way of the California grizzly bear or the jaguar? These are choices we have to make.”

In addition to pondering pressing questions about the interplay of wildlife and human development at a “conservation action” tent and an interactive “habitarium” at the California Trail, visitors can take a 5-minute Swiss gondola ride above the site, stay overnight in a “safari-style” campground, and take their kids to a new playground or a restaurant at the top of the aerial lift.

Kimberly Veklerov is a San Francisco Chronicle staff writer. Email: kveklerov@sfchronicle.com Twitter: @kveklerov