The pair, who work part-time for Canberra trail builders Iconic Trails, have also been volunteering their time to build jumps and loops at the Majura Pines, a favourite bike hang-out for generations of Canberrans. Harriet started working there alone late last year, literally using a shovel to make the jumps by hand, digging until late into the summer evenings.

Some weeks she spends 40 hours at the site, which she's renamed Majurassic Park - stickers available! - as more and more people have joined her to carve out and pack in challenging and exciting jumps, and as excavators and other machinery have joined the effort, with the support of the ACT government.

"It's lots of hard work but it's fun, though, especially getting on the machines," Harriet "Haz", 24, said.

"I'm up all night thinking of ideas. You can build a trail however you want, if you want to challenge yourself or try something a bit different. You can be really creative with it, not many people realise that. You can express what you want to do on your bike."

Zoe, 19, also a part-time graphic designer, enjoys the camaraderie at Majura.

"It's such a good crew as well. Just good people to hang out with and spend time with, and they all ride as well, which is really cool," she said.

Harriet has been racing bikes since she was four, first on a BMX and then mountain bikes from five years ago. She was sitting top 10 in the world last year in Crankworx, the global tour of mountain bike festivals, when she crashed and couldn't make the final events. BMX Australia describes her as a passionate and courageous rider.

"I started at the BMX track at Melba at four with Canberra BMX, which is amazing now, there's so much more kids now than when I started," Harriet said.

"I think just from a very young age, maybe two or three, my parents couldn't keep me off a bike so they kept searching for things in Canberra where I could ride and they found the BMX track and took me there. It was like, yeah, couldn't stop me."

Described as Australia's top female junior talent in mountain bike cross country, Zoe proudly displays "Ride Like a Girl" on her Instagram bio. She finished fifth in the world in the junior ranks last year. She competed in her first race at seven, at Majura Pines.

"I think I lost my chain and came last but I absolutely loved it and made mum immediately enrol me into the next race," she said.

"So, yeah, I've been riding ever since."

Both women grew up in Canberra, both attending Lyneham High and Dickson College.

At Iconic Trails, which designs and builds walking and bike trails, the girls are busy, especially on lots of school projects, including building pump tracks and longer tracks for students. Majura Pines is something for after work, simply an expression of their love for the sport.

It takes weeks for a jump to be perfected. They are at the upper end of a trend being seen around Canberra, as bike-mad kids make their own jumps in parks and open space around the national capital.

Iconic Trails owner and rider Garreth Paton says both Zoe and Harriet's work ethic is second to none. And their riding makes them excellent role models, especially for girls who might be tempted to give up sport as they get older. He and wife Cara, an accomplished rider, have two daughters, Lexi, 9, and Shilo, 6, and he loves seeing them inspired by women in the sport.

"They're hard workers and amazing riders and my girls just look up to them and are amazed by them," Garreth said.

Zoe says she feels just as motivated being with other female riders.

"I think being able to ride here with Harriet and sometimes Caroline [Buchanan], and all these amazing girls in Canberra, has been so inspiring. Often, there's other kids and little girls riding and it's just so cool to see the next generation come through," she said.

Harriet says she was registered as a volunteer and, with the support of the ACT government, was creating a network of jumps at Majura Pines that was safe and legal.

"This place hadn't been touched for about six years until I came," she said.

"What happened is that Harriet came here and started digging by herself and spending hours and hours here and everyone was inspired by her, about 20 people came to help her," Zoe added.

Harriet added, with a laugh: "They felt sorry for me. We have people coming and helping every day. And there are so many kids here, it's great. That's what we wanted."