That sounds like heat/water stress wilting.

Its probably reached the limits of the size the container can support.

I'm in SoCal as well and having the same issues with my container squash. The wilting is from the heat. Keep them well watered. They can drink the water in a 10 gallon container FAST in this heat. The container also gets the soil hot causing stress. Your container isn't black, is it? If so, paint it or cover it with something a lighter color. Some of my zucchini wilts during the day as well. To some extent, I understand it is normal in the heat. It's stressing everything.

I also have a bad leaf miner issue. I don't worry about it too much on the squash but did cover my container of chard since I want to eat the leaves.

Ania

Ania, thank you so much! The zucchini pot isn't black, but it *is* dark green, so close enough. I covered the pot with a white trash bag and the plant's doing *so* much better; it's hardly wilting at all any more.

iam3killerbs, thanks as well. I don't think it's too big for the pot just yet- it's still pretty small, but I'll keep an eye on it and keep in mind that I may need to transplant later.

You probably cannot transplant the squash later.

Cucurbits -- squash, melons, and cucumbers -- hate having their roots disturbed and are best grown from seed in the place they will spend their entire life.

If they are to be started and transplanted it much be done when they are VERY small -- with only a couple pairs of leaves at most.