'Today is skate day, kiddos!"

Wouldn't that be every day for the horizontally mobile? Not for "Shred the Patriarchy," an informal, feminist-slanted group that has been sending that message over Facebook much of the summer to meet at Paine's Park on Thursdays and Sundays.

This loose collection of women of all stripes - its fliers call for any "female-identified folks" - are hardly typical or hugely welcome among the guys performing sprint-speed feats on boards and bikes.

Shred the Patriarchy, organized on Facebook by 21-year-old philosophy student Sky Kalfus, is there to establish a presence for women in skateboard parks - as well as an opportunity for them to get better.

"I wasn't comfortable skating here by myself," said Kalfus, a native Philadelphian on summer break from Oberlin College in Ohio. "I remind myself that I belong here . . . though people act like I don't."

A self-described "Internet feminist" (feminism as disseminated through blogs and social media), she sees the park as one of many male-dominated spaces: "The entire world is like a skate park, right?"

Also, skateboarding is a bottomless pit of skill - and the stunts can be scarier than any questions about belonging. "You're never the best. You master one thing and there's always something else," says Riley Dalca, 23, a Florida native who took up housecleaning in Philadelphia when she broke up with the girlfriend who brought her here. "This isn't a 'hate-boys' thing."

"Sometimes I feel in the way because I don't know how to skate that well," says Lucy Denegre, 18, who lives in the Fairmount neighborhood.

The park, located near the Art Museum, is a series of slopes and ledges, much of it granite, looking something like the inside of a seashell. Shredding refers to skating to the extreme (though obviously Kalfus uses the word with multiple meanings). Collisions among skaters are inevitable but surprisingly infrequent, whatever the gender or level of skill. But when they happen, the skaters react nonchalantly, often not exchanging a word. Also silent is the scrutiny of the two to seven Shred the Patriarchy women at any given meeting. Guys skate by, their eyes full of questioning.

The women don't try to blend in. Kalfus wears a bright, tie-dyed T-shirt, smart-girl glasses, and a helmet. Others wear bright-red lipstick and eyeliner. Dalca doesn't shave her legs. "People [at skate parks] ask me if I am a he/she," she says in her characteristically imposing voice. Though biologically female, she describes herself as having "transcended" gender.

Claire Coslop, though, is eight months into a male-to-female transition, but that hasn't changed her skateboard habits, which started at age 7.

"It's a hard drug," says the 31-year-old South Jersey native, who suffered an arteriovenous malformation that hemorrhaged and temporarily paralyzed the left side of her body. "I couldn't ride a bike. But my neighbor had a skateboard. I was able to turn on it and make myself go. It's like I was supposed to do it."

Meridian Lowe, 18, a theater major at Temple University dressed in black with skulls and studs, would like to have a destiny on a skateboard, but is too intimidated to try.

"There's all these bros and dudes," she says. "And I have a lot of insecurity about taking up space and learning how to do something that involves my body, falling and making mistakes."

It's a legit fear: One Shredder heard a guy saying, "They're really momming up the place." But others are openly welcoming, like James Wheeler, 18, of North Philadelphia, who hopes to be a graphic design major at Temple University.

"I think it's pretty cool that they're here," he says, adding that the minute they walk into the skate park, they're no longer seen as dating prospects.

Well, not always. Dalca was less than impressed with the helpful tips offered that included a bit of male condescension and less-than-appropriate touching.

Other parks can be more menacing. FDR Skatepark, built partly under an I-95 overpass in southernmost Philadelphia, has unprintable graffiti saying, in no uncertain terms, that beginners aren't welcome. At the Grays Ferry Crescent Skatepark one weeknight, Kalfus and Dalca witnessed a pocket knife pulled among guys in a short-lived scuffle.

Recently at LOVE Park, once iconic to skateboarders worldwide until a ban and $300 fines were enacted in 2000, one skateboarder beat up a ranger who was trying to enforce the rules.

Why even do it? You'll never know by just watching. The first step on a skateboard is like slipping on a hyper banana peel - and something completely contrary to what kids are taught, to keep their feet on the ground and hold on with both hands. It's an exhilarating renegade experience.

Then there's the airborne element, when skateboard somehow levitates with rider. It couldn't look easier, but harnessing gravity with that much precision can come only from years of practice.

Skateboarding's place in the community is "past the point of debate," says Josh Dubin, executive director of Franklin's Paine Skatepark Fund, who welcomes Shred the Patriarchy. "There are issues of misogyny," Dubin admits. "That strain exists in all sports, but particularly action sports. What's needed is to get people in the same room - or in the same park."

As Kalfus hands over the organizing duties to her Shred-mates, it's hard to know how long the group will last. But their presence by the end of the summer had an air of progress. During their last meeting in Paine's Park last week, Kalfus got an extended skateboard lesson. Was he condescending? Touchy-feely?

"Oh no!" she said. "He's an adult!"