Update 1 April 2021. This ride is currently not possible due to the Butters Bridge closure. It gets worse. The detour suggested by CyclingGravel is blocked too.
Crossing the river on gravel is only possible at Coombs.
Namarag Molonglo Special Purpose Reserve construction works have closed the Butters Bridge at its north end. Bridge access is possible from the south end (Denman Prospect) just for the view. (Stand 6 February 2021)
CyclingGravel suggests a ride in Canberra through the Molonglo Valley. While the area is well known to many, the route through Denman Prospect over Butters Bridge is less known and worthwhile. Denman Prospect forest is an old pine forest that survived the bush fires in 2003.
The full article can be found here.
Warning: locked gates
This route along the Molonglo Valley River Reserve has the usual problem with locked gates. The gates are locked to keep cars out. There are many types of barriers that block cars but allow pedestrians, cyclists, and horses easy access. Pedestrians and cyclists are generally permitted in Canberra Nature Park but the gate design does not reflect this policy. A locked gate keeps everybody out who cannot climb over or through the gate, as well as cyclists who cannot lift their bikes over the gate. Locked gates disadvantage those the most who are already disadvantaged. Canberra Nature Park is for everybody.
Here is how it is done in Stromlo. Horses, pedestrians and cyclists can easily pass this locked gate. Cotter Road car park, western slopes of Mount Stromlo, Mount Stromlo Forest.