Note: Described in the reverse direction to your journey
From Cow Creek Saddle the track descends slightly and then sidles in the bush until it opens up at the head of an old and massive slip area. An easy scramble down into the eroded gully and follow the easy open stream-bed down the whole length of this open, and rather attractive area. Cairns and markers make the route easy.
Just before the bush is reached at the lower end, exit up onto the true-left bank and and pick up a marked entry back into the bush. Another 150m or so and Cleft Creek is reached. The map is not quite correct at this point.
Although not essential, it's easiest to cross Cleft Creek and proceed on the northern bank for a short while before re-crossing and picking up the orange markers at the start of the main track that follows easy and pleasant terraces to the Ruamahunga/Cleft Creek confluence. Not highly maintained, but the relatively stable old-growth forest won't claim it back in a hurry either.