Aye, the track that goes up past the fort with the range on the left side would be do-able - I walked some of this with my daughter earlier in the year. Steep at first, and heavily rutted in places, and even though you'd be riding a fair bit further than what we did yesterday, the easier terrain would more than make up for it I think.
Velo, if you want a higher-res version of that photo, give me a shout. I think flickr possibly limits it to 1024 pixels in width? The original from my phone is 2048.