Check out this ride Linda and I did from Mountain Lagoon to Mailes Ridge 2 weeks ago. 

6 kms on locked off firetrail plus 4 kms on single track. The return journey doubles these figures up. 

It had a really nice wilderness feel and everything was rideable plus has great views. Linda and I were rapt. 

It's makes for a good half day ride. 

Could easily convert it into a full day exploration by hiding the bikes at the end of the single track and then walking another 2 kms on a ridge to an old trig (if its still there). 

Or for a full day of just riding, do the above ridge plus another that goes to a lookout overlooking the Colo. This other trail is open to cars ... but it's unlikely you'll see one. 

Cheers, 
Terry