I feel that the problems are drainage issues of the soil, and also over-watering....

EG

It is normal for the leaves on tomato plants to die off from the bottom up as the plant grows. So how old of plants are we talking about? Post-production plants or ones just planted?

"Southern CA fruit well into fall or early winter" wouldn't be normal. You are lucky to have 2 separate tomato growing seasons while much of the rest of the country only has one but mid-summer isn't one of them normally. Your planting and ideal growing times are very different from much of the country.

Maybe in the northern zones, but even here a spring planted tomato plant won't set fruit and continue production well into fall. It is just to hot to set fruit, you get blossom drop, plants get stressed from the heat, pests and disease. That's why we plant fresh plants in mid-late July so they will kick into production once the weather breaks in the fall.

Dave

Agree with engineered...........plants are likely DROWNING.

Try heavy watering, but only once every 5-7 days.

Parts of SoCal have been unusually cool this year like it was last year. However I'm in zone 9b and would have to agree with digdirt if your temps have been high. Tomatoes tend to suffer in the heat of summer in zone 10.

tomatotomata,

Dave knows his tomato culture, so I agree with him. But it is also possible that you are overwatering since that is the most common problem people have with tomatoes. (It can also make them less flavorful and more prone to cracking.)

GardenWebber sprouts_honor (Jennifer from Cleveland) had a wonderful suggestion on how to tell whether or not you need to water your tomatoes, and I quote here: "Get a wooden dowel rod (or two) and sink it in the ground near a plant or two and leave it. Pull it out when you think you need to water. If the top is dry and the bottom is a little damp, it's time to water. If it looks dark and feels saturated, wait to water. I use this technique with potted plants that don't like being over watered and it's helpful with in ground plants too."

Good luck!

Betsy