Twenty miles west of the west coast of the United States lies a string of pearls, a Southern California island chain familiar yet in some ways wildly different from the mainland.

Santa Cruz Island, the largest of the eight Channel Islands, has nearly 150 plant, bird and animal species not found anywhere else. Recently, my wife and I went on a “service trip” to the island, a sort of working wilderness vacation that allowed us to see the island as few others do.

The adventure was one of dozens of Sierra Club service trips around the world each year. Participants pay to gain access to a rare or beautiful corner of the globe, but also to “leave it better than they found it,” to borrow the phrase of trip leaders Dave Garcia and Paula Haydon.

The five-day Santa Cruz Island trip supported another organization, Channel Islands Restoration, which has been removing invasive plants and animals from Santa Cruz and other islands for years. Our days on the island would mix business — conquering the vinca major, or periwinkle, one root ball at a time — and pleasures including a visit to a perfect beach three short but steep miles from an historic ranch that is a remnant of the days of Spanish rule of Alta California.

The journey

The magic began before we landed at Prisoners’ Harbor. Our group of 13 volunteers met with retired California State Parks ranger Garcia, Sierra Club trip veteran Haydon and Channel Islands Restoration leader Ken Owen at Ventura Harbor for a 90-minute cruise to the island.

The boat teemed with fourth-graders headed for the one-quarter of the island maintained by the National Park Service. They oohed and aahed with every ocean swell. The oohs and aahs grew when we stopped to view a humpback whale that surfaced a short distance off the bow, spouting and diving, his (or her) massive tail plunging gracefully into the water.

Two more unusual sea sights greeted us before we reached the island. A school of dolphins arced out of the water by the side of the boat in a steady rhythm, and later surfed in the standing wave of our wake. A few hundred yards away, the metal pipes and platforms of Gail, the most productive of the 19 Santa Barbara Channel oil derricks pumping petroleum and natural gas to the mainland, loomed above the water’s surface.

The students and other day visitors left the boat at Scorpion Anchorage. We headed north to Prisoners’, at the edge of the 72,000 acres of island owned by the Nature Conservancy and off limits to the public.

This would be the last we’d see of the ocean for awhile. Our destination was the central valley, two miles up a leafy canyon under intimidating 1,000-foot canyon walls.

Here, for the first time, the irrepressible enthusiasm and encyclopedic knowledge of CIR’s Owen came into play. He brought our convoy of two Air Force-issue Chevy pickups to a halt several times, pointing out the lovely Humboldt lily growing by the canyon creek, the dun-colored Santa Cruz Island buckwheat and more.

After 20 minutes of jostling on bench seats in the truck beds we reached our temporary home at the UC Field Station. Here, you’d never know the ocean is only two miles away. We traded ocean fog for dry summer heat, seascapes for jagged red-brown volcanic cliffs, fourth-graders for mosquitoes.

Meet the Pulaskis

As much as six hours a day were to be taken up with work, but Owen and his capable aide Kevin Thompson were merciful. Over the five days we clocked perhaps 15 hours of labor, not including help with cooking and cleaning.

Three shifts were spent pulling the invaders— vinca major, which grew along the canyon creek, and red valerian, a pretty pest doing a little too well for Owen’s taste in a vale on the western edge of the central valley.

As the trucks bounced along the trails, Owen pointed out with equal respect his favorites — the coreopsis, what he called a “Dr. Suess plant” that offers a spectacular sunflower, and the tough dudlia candelabrium, a desert succulent clinging to rock faces and sprouting showy red and green stalks — and the bad guys — hemlock, fennel and eucalyptus.

The red valerian grew in and around sage plants and coyote bush at the foot of Pico Diablo, the island’s 2,434-foot high summit. We spent five hours pulling, sawing and snipping at the bush to expose the stalks so they could meet their demise.

Owen’s reward for our day in the weeds was a breath-taking, bone-jarring ride along the Ridge Road, taking in the island’s unique plant species, a coastal pine forest where the Chumash caught drip water from the fog to slake their thirst, and stunning views of the jumbled island topography giving way to the calm blue Pacific.

On another day we built a hiking trail at the edge of the historic ranch, just above a tiny Catholic Church built a century ago and re-consecrated by then Archbishop (now Cardinal) Roger Mahoney in 1991. The ranch was also home to a sturdy adobe building, wooden ranch homes and barns and workshops built of bricks fired on the island.

The compound was bordered by stately lines of eucalyptus, planted to funnel sheep toward the shearing shed now occupied by piles of tools and a colony of pallid bats.

On our day off we marched over the hills to Coches Prietos, a lovely cove on the island’s southeast side. Some tested the water or snorkeled, some explored the marine life, others just lounged in the sun — with no beach crowds in sight or mind. Rugged hills towered over the empty beach, Owen pointed out an Indian shell mound, brown pelicans glided past in search of fresh sashimi in the deep blue waters.

The next day, after we put away the Pulaskis and McLeods (firefighters’ tools used to hack out the trail), Owen led us to La Cascada, a freshwater pool in a desert-scape canyon where the muscle ache and dust from the morning washed away.

The takeaway

As with any sleepover, the camaraderie of the troops was key to the trip’s success. A librarian from New Jersey, two sisters — bold young explorers from Westchester, Pa. — two witty and gentle gents from Santa Fe and several others, we came together easily around the leadership of Garcia, Haydon, Owen and Thompson.

After dinner one night Garcia instigated a game, Two Truths and a Lie, that left us surprised. That mature lady got busted in her jammies on top of a Civil War monument in the wee hours? The erudite lover of the arts used to sling scotch and soda at a leather bar in the Castro? Who’da thunk it?

Owen offered evening slideshows rich with information about the island and restoration work, and shared his library of natural history and island arcana. Garcia offered prizes for participation and general talks on the dangers of bottled water and overfishing.

The work, once-in-a-lifetime sights, outdoors education and esprit de corps formed parts of a whole that made the trip rich, rewarding, memorable.

Two weeks earlier, a corporate group from the North Face had done similar work with Owen, and groups of all kinds can benefit from the island adventure. Visit channelislandsrestoration.com to learn more. Garcia is only one of many capable guides who runs exotic service trips. To learn more, visit sierraclub.com.

I grew up in L.A., moved north a long time ago and have pondered the Channel Islands many times while tooling along Highway 101. I’ve finally gotten a taste of life west of the west, and I won’t soon forget it.

(Note: The author’s wife, Elisabeth Frater, is chair of the Napa group of the Sierra Club.)