"Yes, it is a bit noisy here, isn't it," replies Beveridge, Convenor of Friends of Black Mountain, at the top of her voice, valiantly attempting to compete with the persistent noise of passing traffic.

Giving up yelling, Beveridge soon resorts to hand signals motioning me in an unexpected direction towards a culvert which runs beneath Glenloch Interchange.

Careful not to step in puddles of water which obstruct part of the track, I carefully follow Beveridge into the circular culvert.

Inside, well shielded from the traffic noise, it's much easier to hear my guide. "Everyone loves a tunnel, don't they," she says while ducking beneath cobwebs and past swallow nests.

The tunnel is about 60 metres long and as we emerge from the abyss and into an area of natural endangered snow gum woodland Beveridge announces, "welcome to our hidden island". And in a way she's right, surrounded on all sides by the spaghetti-style off-ramps and bi-ways of Canberra's busiest interchange, it's a special patch of remnant native vegetation among high-volume traffic flow.

"Not far now", remarks Beveridge who is leading me to an ancient snow gum (Eucalyptus pauciflora) several centuries old which continues to grow in this most unlikely of places.

Along the short walk to the tree, Beveridge, points out other native species. "Look, there's a native cherry [Exocarpos cupressiformis]", she reveals before bending down to show me the delicate leaves of a Daphne heath (Brachyloma daphnoides) and highlighting "the interesting way the leaves form a sort of cup cluster at the tip".

A few more steps, and just beyond a patch of Urn Heath (Melichrus urceolatus) resplendent in creamy-coloured tight flowers, looming ahead is the grand old snow gum.

What a sight! Twisted and gnarly, with yellow swirled bark saturated from recent rain, it stands sentinel to dozens of its progeny which have sprouted up around it.

Beveridge stands back and gazes up at the trunk, which is over three-metres in girth.

"What I really love about this tree are all the patterns with the burls and branches and the way they hang," she says. "Often I see a face or abstract shape such as an animal in the branches".

Seeking shelter form a passing shower in its partly-burned hollow, Beveridge explains: "This snow gum was first highlighted as a notable tree by Lindsay Pryor and John Banks in their definitive Trees and shrubs in Canberra (Little Hills Press with the co-operation and assistance of the ACT Government, 1991).Local residents and environmentalists then saved it from chainsaws when the Gungahlin Drive Extension was carved out of surrounding bush in 2004".

Despite the proximity to the highway, this island is home to a surprising diversity of wildlife. According to Beveridge, "We often see butterflies and small birds fluttering about and on one memorable occasion a flock of about forty noisy yellow tailed black cockatoos landed on surrounding trees." They must have been loud for, according to Beveridge, "they even drowned out the traffic." An effort which, as yet another truck rattles past City-bound, would be no mean feat.

This island has been a well-kept secret for many years, but Beveridge and her fellow Friends of Black Mountain are looking forward to sharing it. "We are hosting a walk to the tree as part of the upcoming Canberra & Region Heritage Festival," she says. "It will be a rare opportunity to view this special part of our living heritage."

Indeed it will. I tip my hat to the members of the Friends of Black Mountain and prior to that Friends of Aranda Bushland, who in conjunction with ACT Parks and Conservation Service have ensured that this roadside treasure stands tall for future generations to admire.

Tree tales: On Sunday April 23, 9.30am to 11.30am, you can join local conservationists Jean Geue and Linda Beveridge to discover this hidden ancient snow gum during a special Canberra & Region Heritage Festival walk to mark the significant natural heritage of this traffic island. Although total walking distance is less than a kilometre, it is on uneven ground. Children are welcome if accompanied by parents. Bookings are essential. Email friendsofblackmountain@gmail.com or phone Linda Beveridge on 0437 298 711. The event commences from the stile at the entrance to the Aranda Snow Gums and Frost Hollow Walk near the Glenloch Interchange. Detailed directions to the start of the walk will be provided on booking.

Cost: Gold coin donation.

Don't forget: BYO morning tea, hat, and sturdy shoes.

Warning: Always exercise caution when walking near culverts, especially during or following rain.

Did You Know? The snow gums below the Aranda Bushland which include those in the Glenloch Interchange 'island' are some of the last survivors of what used to be a continuous ring of snow gums encircling the frosty, treeless flats of the Molonglo River.

If you've driven along Fairbairn Avenue near the airport anywhere near peak hour, you don't need me to tell you that it's one of our city's busiest roads.

In fact, most motorists are so focussed on negotiating the traffic they don't even notice a short bridge that crosses Woolshed Creek just near the off ramp of the Majura Parkway onto Fairbairn Avenue.

It's a pity, for beneath this bridge is an ancient treasure trove of marine animal fossils, that when discovered by renowned geologist Reverend W.B Clarke in 1844 were regarded as the oldest fossils in the entire country. Some of the fossils which include brachiopods, trilobites and corals were recognised by Clarke as belonging to the Silurian (419 – 443 MYA) geological period, an exciting discovery indicating for the first time that rocks of this age were present in Australia.

Back in 2011, when this column first highlighted this fossil find, it bemoaned at the difficulty of access. However, I'm pleased to report that as a result of an ACT Heritage Grant and with support from Roads ACT, a brand new pedestrian path has been built along the banks of the Woolshed Creek which provides access to the fossil site without having to run the gauntlet of dashing across the road.

This column shares the enthusiasm by the Geological Society of Australia in hoping that the improved access "will enable visits by students, teachers and the public to continue for many years to come."

Woolshed Creek Fossils: Located under Woolshed Creek Bridge on Fairbairn Avenue.

Although it won't be officially opened until later this month, curious Canberrans can take a sneak peek at the newly rehabilitated site by following the new walking path along Woolshed Creek. To access the path, park near the end of Hopkins Road, Duntroon, and walk through the underpass beneath the Majura Parkway. About 50 metres on your left you will see a sign and the brand new 150 metre long path which leads directly to the site.

Did You Know? During road work on the bridge in 2010, large rock specimens with fossils were excavated by the building contractors and set aside for scientists to study. One of these now takes pride of place in the foyer of Geoscience Australia's headquarters in Symonston.

Cryptic Clue: The science of collecting autumn leaves can be a tricky one.

Degree of difficulty: Easy - Medium.

Last week: Congratulations to Stephen Esdaile, of Ngunnawal, who was first to correctly identify last week's photo, as "the suspension bridge on Keirs Road just outside of Murrumbateman, not far from Helm's Wines." Ken Helm, a regular reader of these pages advises he "got the residents together to build the bridge in 1981 as before the low level crossing was raised we would be flooded in on a regular basis," adding "the plans for the bridge were developed from the ruins of a similar structure located about two kilometres upstream and built by Hector McIntosh in the 1940s."

Meanwhile, Peter Hughes, of Forrest, who previously lived near the bridge admits he also played a role in the bridge's construction. "It was designed so that if it rained heavily during the day Canberra commuters could park our cars on one side and then walk home."

However, it appears the bridge never had much use, for according to Hughes, "after it was built we never really had the same amount of heavy rain and I never actually used it."

How to enter: Email your guess along with your name and address to timtheyowieman@bigpond.com. The first email sent after 10am, Saturday April 1, 2017 with the correct answer wins a double pass to Dendy cinemas.

CONTACT TIM: Email: timtheyowieman@bigpond.com or Twitter: @TimYowie or write c/- The Canberra Times, 9 Pirie Street, Fyshwick. You can see a selection of past columns online.