When I walked this route in 2007 the land up Birch Hill Stream was claimed by Glentanner Stn. However, looking at WAMS it is clear that the north bank are DOC / LINZ land as far as the third sidecreek on the south, above which all land is DOC. This is a high pass with a 1600m ascent on tussock, snow and stable scree. It climbs snow chutes and would be dangerous in avalanche conditions. A good challenging late-summer route alpine route requiring ice axe, and recommended with crampons.
From the road bridge head up the north bank of Black Birch stream. All land on the north side is crown land either under DOC or LINZ. As the valley steepens, follow the main creek up, travel on tussock. As you hit the steepest section at around 1400m, take snow/scree chutes on the left-hand (southern) side of the valley. This chute curls round behind the cliffs that appear to block the centre of the gully and lead to gentler scree faces above. An ice-axe was handy on the steepest snow sections, and crampons would have made things easier.
Once at 1600m, past the steep section shown on the map, travel is straight forward up scree slopes to the pass. The last section to the pass holds snow year round but is gentler than lower slopes and ice-axe alone was sufficient in late summer.
Good views of the upper Dobson are available from the top - 1000m vertical cliffs topped by glaciers under which you must pass to descend the Dobson. (3-6 hrs)
Follow boulder-scree slopes down into the upper Dobson. Follow the river down, avoiding exposure to ice-falls from above where possible. The valley floor is littered with chunks of glacier that have come crashing down - do not linger. OK progress on recent moraine. (1.5-3hrs)
After 1.5km the valley broadens and the danger recedes. Moraine is replaced by rounded river rocks and the banks change from rock to tussock. The Hour Glass Glacier provides a spectacular backdrop to the head basin of the main Dobson valley - another ice plateau clinging above sheer bluffs. Follow the river down another 1.5km to the main forks, then another 1.5km to where the V shaped valley broadens to wider flats. Head east away from the river along the scrubedge at the head of these flats and nose around to find Reardon Hut in the 2nd basin. An amazing spot with bare ice and rock behind, valley flats and cows ahead. A point of contrast. (2-4hrs)