I'm sorry to hear of such a sad & strange occurrence.

Any chance of pictures, especially of the remains after they've fallen? Are the bottoms of the plants which have fallen over soft & mushy? Can you see roots exposed & perhaps describe them? Are they soft, brown & mushy?

Do you observe similar behavior among other plants in your neighborhood? Have you spoken to any neighbors? Can you try to consult w/ any local nurseries?

I would guess it's as you say - they're too lush / overwatered / no support and they're falling over due to top-heaviness / lack of root-ball (sufficient to support the plant).

Yes, I too would be liking to see pics of it.

As an FYI, there's precedent for this mass falling of trees / shrubs (involving fatalities, unfortunately). It's been found that mature Eucalyptus need to be not irrigated, because if they are their roots stop growing out, thereby depriving the tree of sufficient extensive rooting (both down but especially out away from the tree) that the tree eventually topples over - this can ruin one's day when the tree is nearly 80' tall and weighing scores of tons.

I agree with the above two posters, as my immediate thoughts were that these plants are loosing their neighbourly support. Being on a hillside, there will always be a strain on the roots for them to hold themselves upright. Gravity will take over when the adjacent plant falls as they are not lightweight and can be top heavy as you know. From what I know about jades I dont think they have a tremendous root system, which wont help their dilemma.
Its a great shame this is happening as I can imagine they are a sight to behold, but we would all be intested to see a pic if possible please?
I do hope you can find a solution and save the remaining plants. Perhaps staking them on the top side may help or piling some spare soil or even rocks around the stems on the lower side of the slope? Just a thought or two!
Gill from the UK.

Hi everyone, thanks so much for your replies! Looking online, it seems like over-watering is the most likely culprit, but but as I said, they haven't been watered, except for rainfall. The rainfall was pretty heavy last year, but I would be surprised if it's still affecting them 7 months later. Anyway, here are some pics to give you all a better idea...

This first one is of an area where the jades are all still standing, so you can see what the area is *supposed* to look like:
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And here is a pic of a freshly fallen jade, so you can see the stump left behind. It was moist, but doesn't seem spongy or rotten.
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And here is a photo of an area where a bunch of them have fallen down, so you can see the damage.
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I have this weird feeling that your plants were a little top heavy, then maybe got too dry, slumped over, and with the slumping and the weakening of the trunk due to dryness, they snapped off. I would have gone with what Jeff said about the root-ball, but you have a stump. The neighborly support, chain reaction makes sense in this context as well. If this seems right, I would recommend a trim and slight increase in watering. Crassula ovata will grow in clay soil but the root system can remain small and shallow. This means it can dry out and suffer in a long, hot stretch.
I'm still somewhat of a beginner so don't print this in the encyclopedia.
Maybe someone else can help confirm or collapse my suspicions.

Maybe like a beaver or something.
Can we see a close-up of the stump(s)?
Are the stumps rotted or are they alive?

I think they stretched upwards a bit from being so close together, too, making them less stout, less strong and less stable. At least that is what the first picture suggests to my eyes, where they're still standing.

Hi...
I guess I would add have you been having windy days or nights..that would tip over trees....
what a beautiful view you have.....linda