This information was provided following responses from Colin McDonald and Brian Bere-Streeter - the information coming from "38" by John Thompson, Eveleigh Press, 1992 - Chapter - 'Off the Rails'
The accident happened at approx 4.05am [probably 5.10am] 30th June 1948 when 3817 hauling No 23 South West Mail between Rocky Ponds and Cunningar was derailed by a broken rail. Four persons were deceased
and twelve seriously injured. [see below for a later update from Trevor Edmonds]

Brian's Summary - "3817 had an unfortunate career, as it was also involved in two other accidents -

30th Oct 1959 - near Aylmerton - 3817 hauling No 128 fast stock train stopped in a cutting due to torrential rainfall, the crew tried to reverse the locomotive out of the cutting without
success, and sensing danger left the locomotive and walked to a safe position - shortly after, a wall of water around four feet high flooded the cutting, washing away the embankment
under the locomotive, which slid nose-first into the resulting hole at 45 degrees.

23rd Aug 1963 - Geurie - 3817 hauling No 58 Mail collided at speed with Garratt 6003 which was shunting and partially fouled the main line  - 3817 was called the 'Voodoo' engine
because of its three major accidents, and withdrawn from service immediately - both locomotives were extensively damaged and were deemed uneconomic to repair and subsequently
scrapped. Twenty persons were injured requiring hospital treatment."

Trevor Edmonds has contacted me with the following updated information (Nov 2012).

Trevor says: " Your time of 4:05 is incorrect. At that time the train was at Yass Junction and was on time. The last accurate time I have for the trip comes from the guard Henry Turner, who gave the departure from Galong as 4:58. Given the driver, Ernest Nolan, tended to take the curves between Galong and Spring Creek slower than the posted speed I am giving 5:10 as the approximate time of the derailment.

The casualties were 4 killed, and 19 treated at Harden Hospital. Of the 19, one was flown to Sydney for specialist orthopaedic treatment and 12 were admitted. The others were treated and discharged. Only one of the injured was described as serious. All the injured made a full recovery, a result that the coroner credited to Dr Cyril Macintosh who was a passenger in the EAM sleeper. He was THE ideal doctor to have on a mass casualty accident site.

3817 had four incidents. The one you are missing was at Eveleigh Depot in 1949. It did not get publicity because it was out of public view, but the damage was worse than Aylmerton. The chronology for Aylmerton was the train came out of Aylmerton Tunnel and ran into water on the embankment. The driver slowed and then stopped when he felt what was probably ballast on the rails. 3806 was approaching with (would you believe) the South West Mail. 3817's driver tried to stop 3806 by whistling, but was ignored. The four foot wave was the wake from the South West Mail. There was then some subsidence and the unsuccessful attempt by 3817 to back out. The crew then abandoned the locomotive and climbed the cutting: just before the big washaway.

The reason the driver of 3806 ignored the warning? The train had been hit with a mudslide. Its driver was (I believe) trying to get a train full of injured and very wet passengers to Mittagong for help. He could not afford to stop and become marooned in the bush.

The name given to 3817 after Geurie was Hoodoo Locomotive (Sun Herald 25 August 1963). Voodoo engine implies it could do black magic. Hoodoo engine means it was cursed."

Many thanks Trevor.