There are OpenStreetMap updates for both Mount Mugga Mugga Nature Reserve and Isaacs Ridge Nature Reserve. Unfortunately, no new paths come out of it. One route is now closed down to Mugga Lane as a result of new fencing along Old Quarry Road. Big trucks come labouring up this hill all day long. More about the changes below.
In 2015 a study was carried out for the ACT Government reviewing mountain biking in Long Gully Pine Plantation. The report is attached and holds many interesting details. The Spine has been mentioned previously as it is accessible to everybody. It is certainly worth a look. The route “Isaacs Ridge peak from Woden Bus Station” follows The Spin up the hill.
Ride a good bike path, flat and fast gravel, climb a hill or singletrack, and combine it as you wish. There are advanced downhill routes, too, but that is for another day. These rides centre around the Long Gully Pine Plantation at Isaacs Ridge.
Canberra Nature Park makes it possible to ride through a network of reserves that are interconnected without ever crossing a major road. One of these areas is in the south east of Canberra.