Perhaps root rot.

Whenever a whole plant suddenly looks stressed look for root problems. Do not hesitate to dig in the soil to find the problem before you lose the plant. Al

So, I did some digging.

Instead of the rock hard concretey soil I expected, I found it softer, not-quite-damp. Lots of small to medium roots going down and out. Some larger ones that I couldn't figure out. The plant is 4-5ft tall.

Let's just say I gave it one heck of a massage. Whether it will be its best massage, or just its last, is anyone's guess.

Thanks for the suggestions.

Don't dig it up yet, and don't over-water them. Many Ribes go stress-deciduous during the summer. More info here...

http://www.laspilitas.com/blog/post--20--my-ribes-is-dead-so-i-pulled-it-out%2521

Funny, I was just about to post about something similar.... mine is a two year old, didn't flower this year and leaves brown but not dropping off .... I will dig mine up and have a look-see....

just had the same problem, had a two year old plant which went all brown and leaves crispy. Removed it and planted A new one, not even 2 months and half of it seems to be dead and other half green and brown. It is in a shady area so might move it and try to improve drainage but it’s clay below so difficult. Is there a chance to revive the plant or is it doomed

Two days ago I was at a local nursery, Summerwinds in Palo Alto, which has a largish native section. I saw many plants with crispy browned leaves. In particular the whole inventory of Ribes malvaceum ‘Dancing Tassels’ exhibited leaves like that. Late summer into the fall rains is the dormant period for many California natives and it’s natural for them to look that way. It’s the equivalent to winter dormancy in temperate zones.

Ok thanks... mine are all still hanging on in there, I'm in cloudy old England by the way!

I’ve heard about California natives being grown in England and wondered how they managed all that summer rain. I have had some nurseries advise me to water my natives with teaspoons in the summer! Because they can be so sensitive to fungal diseases in wet hot conditions.