If music flows in the heart of Picture Rocks, Hummin’ and Strummin’ is its pacemaker.

The informal jam group — which includes guitarists, banjoists, fiddlers, singers and yodelers — gathers Thursdays for scheduled jam sessions played to packed houses. The number of members varies, but generally ranges in the teens.

There’s usually no pre-set routine or set list. A musician takes the lead in open-mic style, and others improvise on the fly, complementing his musical direction.

All forms of music are welcome, but usually the tone sticks close to country, folk and jazz.

Picture Rocks is an unincorporated community in Avra Valley, near Saguaro National Park West and North Sandario Road.

The group was founded in 2002 by Carol, Larry and Randy Brooks, Deb Hume, and Merrillynne Prohl. The founders are family. Carol and Larry Brooks are married, and Randy is Larry’s brother. Hume is Randy’s wife, and Prohl is Carol’s sister-in-law.

In addition to the Picture Rocks Community Center get-togethers, the group also plays at weddings and community gatherings.

Tonight’s free event goes from 6:30 to 8:30 p.m. at the Picture Rocks Community Center, 5615 N. Sanders Road.

Della Grove, 65, has been singing with the group for three years. She’s impressed with the talent in the group, which is made up mostly of retirees.

“The amount of talented people getting up there is amazing,” she said. “A lot of these musicians have known each other a long time, too. They aren’t snobbish about it. They welcome anybody.”

Carol Brooks, 66, who emcees the event, said the anniversary event will look back at the group’s beginnings. She’s invited former members and memorable guests to bolster the sense of nostalgia.

“We’re going to make a real fun night of it,” she said. “I’m bringing back a guy with a washtub he played as a bass, a tap dancer and a couple who dress as hippies to sing ‘California Dreamin.’”

Brooks, who was recovering from the flu last week, plans to be part of that fun by interacting with the audience and keeping the mood light and freewheeling.

“I do everything ad lib and have fun with everybody. They appreciate when they know you’re having fun. I don’t make anybody uncomfortable. I just tell them some jokes,” she said.

Randy Brooks, a 68-year-old who plays guitar and sings, said Hummin’ and Strummin’ is a social glue for the community.

“It’s a focal point for socialization,” he said. “Some elderly folks don’t get the chance to do much with their abilities or get out to see many things. But they get together Thursday nights. This has become something greater than we anticipated.”

Carol Brooks is also humbled by the group’s popularity.

“We draw people from all over Tucson. We’re pretty well-known. It’s just great,” Carol Brooks said, turning her attention to what she enjoys about participating in the group.

“It makes me feel good. There’s nothing better than music. Some of them can’t sing worth a darn, and some sing so good it surprises you. Some are getting so hard of hearing you wonder how they’ll even hear the next beat, but the crowd loves it.”

Contact reporter Phil Villarreal at 573-4130 or pvillarreal@azstarnet.com