The Flat Top Hill circuit crosses Butchers Dam and follows the interpretive loop along the shoreline passing old mine workings from 1862 and exposed ancient soils. Leave the interpretive loop at the sign to Flat Top Hill and follow the orange then blue markers to the top of the hill. You'll gain 200 metres, mainly on singletrack which at times is quite steep.
There is a four wheel drive track heading north along the crest of the hill which, indeed, is quite flat topped. It's flat because the layered schist rock, uplifted from below prehistoric seas, is still horizontal here. Schist underlies most of Otago. Up on top of this arid hill you get to see it exposed in all its naked splendour.
As you go along the four wheel drive track keep your eye out for filaments of singletrack that hang off it. At times the singletrack is challenging. There are some rocky downhill segments that will thrill an advanced rider, a few jumps and a short steep section down an unsteerable rut! And all along the top there are panoramic views - the dam and the highway down one side and the steep, deep gorge of Roxburgh Lake on the other. And up ahead you'll see the Manuherikia Valley and the Hawkdun Range.
Eventually, the trail seems to be heading down towards Roxburgh Lake. That's your signal to swing left and head back down to Butchers Dam. However there is a trail that goes down to Roxburgh Lake called Rock of Doom. It's a steep and exposed downhill trail with some serious drops. From the bottom you will have to take the Roxburgh Gorge Trail back to Alexandra.
The trail is not clearly marked and there are a number of four wheel drive tracks. Finding your way is part of the adventure.