Hikers and mountain bikers scattered throughout the forests and glens of expansive Joaquin Miller Park on a recent Sunday afternoon suddenly heard an extraordinary sound: the blast of the shofar — or, more accurately, about 30 shofars in unison.

In a sun-splashed meadow in the hilly Oakland park, more than 750 people had gathered to welcome the High Holy Days with a late-afternoon Erev Rosh Hashanah service on Sept. 13. The park’s 500 acres are heavily forested with redwoods, oak and pine trees, and the tree-ringed Pinewood picnic area made for a glorious setting.

“Best possible way to ring in the new year,” one attendee wrote on Facebook. “Thank you, Tawonga.”

“This picture I’m posting does not capture how beautiful and enjoyable the service was among the trees, but I’ll share it anyway,” wrote another.

The gathering has grown by leaps and bounds after starting in 2009 with about 15 people at Tilden Park in Berkeley. Deborah Newbrun was one of the early organizers, and because she was a longtime director at Camp Tawonga, she decided before year five to bring Tawonga into the mix.

Thus, many of the attendees on Sept. 13 were parents and children affiliated with the Jewish summer camp in Tuolumne County. The requested donation to help defray costs was $36 per family, although paying was not mandatory.

“We’ve been a partner of this event for three years, and it’s a beautiful way to come together to welcome the New Year,” said Jamie Simon-Harris, camp director at Camp Tawonga. “People are excited about three things: being together with their Tawonga friends, praying outside and the service leadership.”

The leaders were Newbrun, Torah scholar Sue Reinhold and song leaders Isaac Zones and Maya Abramson. The service began at 3:30 p.m. and lasted until apples and honey sticks and challah were devoured at about 5:30 p.m. — a couple of hours before the actual start of the holiday, but no less infused with a Rosh Hashanah spirit.

People sat on blankets or low-backed lawn chairs, dancing and singing and praying. On the fringes, parents kept a watchful eye on their children as they frolicked on the lawn, jumped from log to log or slipped in loose dirt while trying to kick a soccer ball. Musicians performed many songs, with lyrics such as “My roots go down, down to the earth” and “You’ve got to change your evil ways, baby.”

All of it had the feel of a bluegrass music festival in the redwoods.

“It was hardly strictly synagogue,” said Rebecca Meyer, associate camp director at Camp Tawonga.

The aim of the service, organizers said, is threefold: to strip away the formality of a synagogue service, to make one of the holiest moments of the year accessible to people who might not attend synagogue and to bring Camp Tawonga-like experiences from the Sierra foothills to the Bay Area.

“At a synagogue, it’s a lot of listening, and you do quiet thinking,” Newbrun said, “but people want the opportunity to bring their whole selves to the service. Our informal outdoor setting puts Judaism in the hands of the people.”

Another aim was getting to the heart and soul of the day, and to that end, many of the songs had to do with the earth, nature and the spirituality of the everyday. At one point, Newbrun went into the crowd with a microphone to ask people about the simple miracles in their lives. Then people were invited to the front to blow their shofars, and after that, more than 100 kids were shepherded across the meadow for kids’ activities.

“It didn’t start as a big event,” Newbrun said of the roots of the gathering. “One of my kids — she was 8 then — asked why we had to go to a synagogue on Rosh Hashanah, why we couldn’t go blow a shofar in a park. And I thought, why not?”

Newbrun continued, “I worked at Camp Tawonga, where I’d started the outdoor service. I had been a national park ranger. I had even written a book, ‘Spirit in Nature: Teaching Judaism and Ecology on the Trail.’ So why couldn’t we go blow a shofar in a park? We called our friends, and 15 of us met at Tilden Park in Berkeley. We called it the Tilden Minyan.”

After Camp Tawonga’s LGBTQ family weekend in 2010, attendees were invited to the Tilden Minyan Erev Rosh Hashanah service at Tilden Park. “And that year we had 50 people,” Newbrun said.

That same year was exciting for another reason: actor-singer Mandy Patinkin attended. At the time, the tenor was starring in “Compulsion” at Berkeley Rep, and Newbrun knew him from Hazon, where she was the was the Bay Area director; he was on the national board. She invited him during a hike in the woods.

Patinkin not only attended; he sang. (For a video, visit www.tinyurl.com/tilden-gathering.)

“Our last song was Leonard Cohen’s ‘Hallelujah,’ ” Newbrun recalled. “Mandy just walked up to the front and started singing, and I remember thinking, ‘Here I am standing and singing between Mandy Patinkin and [recording artist and longtime Tawonga song leader] Isaac Zones.’ What an unbelievable moment for everyone, but particularly for me.”

A couple of years later, the service drew about 250 people, and when Camp Tawonga came aboard, attendance doubled. Because of restrictions against sound systems and inadequate parking, the service had to say goodbye to Tilden Park after last year.

“This is all a labor of love, a fun thing to do,” Newbrun said. “My hope is that we can always hold space for everyone who wants to be there, and still touch each person.”