[1][2] For almost a decade, from 1893 to 1902, Mangaonoho was important as the northern terminus of the NIMT's southern section; even a refreshment room was planned.

Unlike many other NIMT construction camps, Mangaonoho gradually declined after the line was completed.

[3] The 3 mi 70 ch (6.2 km) extension from Kaikarangi (or Rangatira as it then was)[8] was contracted to Cleghorn, Forest, and Magee of Auckland, in 1890, for £26,499[9] and vested in the Railway Commissioners on 14 April 1893,[10] regular services ran from Monday 1 May 1893[11] and a daily train ran from 4 December 1893.

[17] Mangaonoho didn't feature in revenue statements after 1904, when the staff was down to 1,[18] though 6,662 tickets had been sold in 1903, but only 33,000 board feet (78 m3) of timber were railed out.

In 1911 one cottage was moved to Te Wera and another to Whangamōmoana – requesting authority £131.10.0.Approval to remove the station building was given in 1971.

[3] Mangaonoho Public Works Department workshop opened in 1896,[20] 1.37 km (0.85 mi) to the north of the station,[21] on what was Waterfall Rd[22] (now Ironworks Rd),[23] where a passing loop for 67 wagons[3] remains.

[26] The lining of the tunnel was completed in August, except about 15ft kept open to enable the men to run the cutting to spoil.

[30] Like the river, the stream is incised into the soft late Pliocene to early Pleistocene sediments, which are part of the Whanganui Basin.

[20] The viaduct was strengthened around 1932 to allow for the heavier K class, by adding intermediate vertical struts to the Warren trusses of the two main spans.

The viaduct was again strengthened in the early 1980s to prepare for electrification, by replacing the smaller end spans, replacing wooden beams supporting the track with steel, and adding links to transmit traction and braking forces into the main structure.

[32] A $1,403,897 1984 contract by John McLachlan Ltd. covered the deviation,[33] which straightened the line and bypassed No.8 tunnel with a large cutting at a lower level, built by Ian A. Martin Ltd at a cost of $853,461.