Distance: 3.4 km (3.0 DOC hours) - Unmaintained track - Easy-moderate terrain
Altitude: 542m to 1468m. Gain: 36m. Loss: 962m . Gradient: 17 deg
Skills:

Unmaintained track (5/9)
Former track, overgrown - markers / ground trail still followable

Primary, mapped (1/5)
Formal route, on maps, principal access to hut or along range / catchment

Unknown (difficulty: 0/5)
Not specified

Easy-moderate (difficulty: 2/5)
Tussock / river-gravel / open bush / cut track

Unknown (difficulty: 0/7)
Not specified

Unknown (difficulty: 0/6)
Not specified

Unknown (difficulty: 0/7)
Not specified

No description

Note: Described in the reverse direction to your journey

Taken from Paul McCredie TTC trip report
https://www.ttc.org.nz/pmwiki/pmwiki.php/TripReports/2021-01-08-TriangleSpur-MtDundas

Starting at Avalanche Flats, where there used to be a hut, and head up Triangle Spur.
The old track up this spur is no longer maintained, but still has good travel, with even some markers in its lower reaches.

Getting through the scrub belt was no problem.
Before the Dora Track over Pukematawai was created, the route to the main Tararua Range crest in this area used to go up this spur, after coming up the Ohau and over Deception Spur.

Over Triangle Knob and up to Mt. Dundas.