Happy Valley Landslides

Those landslides look fresh, the trees haven't regrown, and there's no sign of drainage channels across the exposed slopes.
This makes me think it's shortly after the landslides in 1966, but that's a guess as well.

It is indeed the landslide on 1966-6-12 at Victoria heights on Stubbs road (upper) which killed the assistant education secretary and his family. More information here:

https://gwulo.com/atom/34387

You can see a large group of buildings at the center of picture above the race course. They belong to Tung Shan terrace on Stubbs road (lower). Above Tung Shan terrace there is a lone black building with white edges which was the Victoria heights.

Here is another picture which offers a close up view of that incident. Below that building is the famous King Yin Lei.

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One can see from the pictures the damage to the building caused by the landslide on 1966-6-12. News report said one of the 4 main beams supporting the building was broken.

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What is surprising is that the victoria heights was still standing around 1970 after the 1966 landslide.