Lambs abound at Stemple Creek Ranch at this time of year.   David Briggs

A lamb will be born on the rolling hills of Stemple Creek Ranch nearly every day through Valentine’s Day. Although the births rarely require assistance from fourth-generation Tomales rancher Loren Poncia and his crew, raising lambs on open, organic pastures involves vigilance, problem solving and care. 

The flock of around 700 sheep represents several breeds—Dorset, Hampshire and Perendale—that are known for both their wool and meat. A number of Bay Area restaurants showcase Stemple Creek lamb, and Coyuchi buys the wool. Although the flock makes up just 7 percent of the ranch’s livestock sales, with the majority brought in by beef cattle, it plays an important role.

“It’s really good for the soil to have multiple species graze the grass. Different species have different impacts on the soil health, considering they eat differently: Sheep go for the shorter stuff, and cows the taller stuff,” Mr. Poncia said. 

Stemple Creek pastures are sown with a variety of drought-tolerant, nutrient-dense crops like rye grass, clover, chicory, plantain and burnet. Pastures are allowed to rest and, in the driest months, livestock are moved to leased lands in Humboldt, Stanislaus and Shasta Counties, where the grass stays green longer. 

As Mr. Poncia drove over his pastureland on Saturday, he kept his eyes glued to the ground, observing: “I don’t know if I’ll ever be satisfied with the amount of diversity in my pastureland.”

Stemple Creek was one of the three local ranches that pioneered the work of the Marin Carbon Project, experimenting with practices that increase the capacity for vegetation to capture and store carbon in the soil. Based on nearly a decade of data, Stemple Creek is sequestering the equivalent of around 1,775 metric tons of carbon dioxide a year. 

Rotational grazing is at the heart of Mr. Poncia’s ethic: Depending on the time of year, he moves his livestock up to 10 times a day. The hope is for the animals to spend enough time on the land to break down the forage and drop manure as fertilizer, but never long enough to leave the soil without photosynthesizing vegetation.

Raising lambs is a longstanding family tradition. “Thirty years ago, my dad’s mom, Nani, started with a couple of baby lambs. She loved raising animals, and she took care of them, nursing them and making sure they were happy and healthy,” Mr. Poncia said. “Her project kept growing and growing: Lamb on these West Marin pastures is some of the best in the world.”

On Saturday, Mr. Poncia greeted his oldest daughter, Avery, who was leaving the house as the last light was spreading over the hills. “To visit the lambs,” she said with a smile.

Mr. Poncia’s wife, Lisa, the ranch’s general manager, said her daughters take advantage of watching the lambs roam and play, though they know what to expect. “They have known since they were old enough to talk, listen and understand where their food comes from. That cycle of life is something we are all comfortable with,” she said.

Lambing season takes place between Thanksgiving and Valentine’s Day, and usually yields around 500 animals. After one year, when the ranch lost 45 lambs in 30 nights to predators—coyotes, red foxes, bobcats and ravens—Mr. Poncia invested in two Akbash and Maremma dogs as guardians. 

Salt and Pepper resemble the sheep themselves, with thick, wooly coats, but they stand taller and possess the warm demeanor of house cats. The dogs have never spent a night indoors, protecting the lambs around the clock. Still, predators take around 15 lambs each year.

Oscar Rojas, who has worked at the ranch for the past 15 years and is one of 16 staffers, focuses on the sheep alongside Mr. Poncia, putting in 60 hours a week. “I recognize each of the sheep by now: I know them,” he said. During lamb season, he increases his vigilance, monitoring fences carefully, searching for any holes dug by hungry coyotes and making sure the dogs don’t wander. 

Once the lambs reach 100 pounds, they are harvested at a slaughter facility in Dixon, and Golden Gate Meat Company in Richmond prepares the meat for sale. 

Mr. Poncia’s legacy runs deep in Tomales. In 1897, his great grandfather, Angelo, immigrated from Garzeno, Italy and bought the original acreage in Tomales, where the family has ranched ever since. The schoolhouse where he went to preschool is now his home.

He moved back 15 years ago and quit his day job. Making a living ranching had seemed like a pipedream, but, he said, “I told Lisa, ‘I’m perfectly happy to go home and fail, but unless we try, I’ll never be fulfilled.’”