When: Saturday, July 19, 11 a.m. to 8 p.m.
Where: Petaluma’s Steamer Landing Park, Copeland at D Street
Info: rivertownrevival.com

Founder Kelin Backman didn’t envision the Rivertown Revival to become another Steam Punk party. But the crowds that streamed into Petaluma’s Steamer Landing Park in 2010 had their own ideas.

They dressed for the occasion in a turn-of-the-last-century meets cowboy-circus style befitting the Victorian era in Eggtown.

“It’s not anything we built up or messaged. It’s just that people really love to dress up and it’s evolved naturally into a Steam Punk theme. It’s hilarious,” Beckman, the festival co-founder, said of the regalia, which includes crazy hats, corsets, flouncy petticoats, makeup, parasols and all manner of hybrid dress.

“People just do their own thing,” she added.

“I remember last year just overhearing someone who happened to be walking behind me in full costume saying he just loved this festival because he could come in a crazy costume and no one would take a second look at him. It’s an opportunity for everyone to wear their freak flag.”

While the majority of the 10,000 or so revelers expected for this year’s fifth annual Rivertown Revival fest July 19 will turn out in costume, shorts and flip-flops are also perfectly OK. The main point is to loosen up beside the murky tidal slough that washes up into the heart of Petaluma and is a focal point of the city’s downtown renaissance.

The annual hootenanny supports The David Yearsley River Heritage Center, a century-old barn within the park that is a community center for riverfront activities.

The fest this year welcomes the The Petaluma Craft Guild, comprised of local microbreweries, wineries and distilleries. Some 30 bands will entertain from five stages, including Zac Carroll’s storied band “Front Porch,” a Burning Man fixture.

There will also be an enlarged area for kid’s activities.

Bring your hankie for “The Hitching Post,” a knoll where some 25 couples are expected to tie the knot or renew their vows in view of the river.

Entry is $10, $5 for kids and seniors. Valet bike parking or hitch a free ride on Petaluma Transit to avoid the $10 parking fee. 11 a.m. to 8 p.m. Copeland at E. D. Street. Rivertownrevival.com.