I am not sure how much water they are getting but it sounds like not enough. You said they are watered 3 times a week; 10 minutes of sprinkler watering. Any idea how this translates to gallons per watering?

If there is no "lack of water" problem with the soil as you suggest, I think you need to get an appropriate diagnosis from your Agriculture Extension Service or universities rather than via the Internet.

There is nasty fungal infection making the rounds in California the last few years called Phytophera Ramorum and I hope that is not what the trees have. You may remember about 5 years ago when the government issued a recall of all camellias shipped from California to other states in order to prevent/minimize the spread of the disease. I am not an expert on this disease but someone in CA should be able to assist since a correct diagnosis is important. The little information that I remember indicated that the disease sometimes produced leaf spots that, in some camellia varieties, were not visible unless you viewed the leaf from below. I did not see any spots on your photos but these were mostly photos of the top part of the leaves. I hope you do not have any spots on the underside of the leaves.

If you send leaf samples for analysis, I would include a few fallen leaves, some of the affected ones and healthy looking ones. If the trees are of the same variety, send the samples in a single bag. Otherwise, separate the samples by variety as camellias respond differently to this organism.

In the meantime, apply good sanitation techniques and water well. Throw any fallen diseased leaves in the trash. Do the same with any other plant debris. Replace the mulch with new mulch. Maintain good airflow around the plants. Do not overwater. Water the soil only and do it early in the mornings. Water again (1-2 gallons) when a finger inserted to a depth of 4" feels dry (or almost dry). Clean with 1 part bleach 9 parts water solution any pruners used on these three trees. Post again if there are any new developments, Luis

It has the appearance of Phytophthora ramorum, so be SURE to follow up on what Luis suggested. This is a dreaded fungus-like disease that affects many different kinds of plants, including much loved oaks. This is the 'sudden oak death' disease, if you've heard of it.

Affected plants can't be cured, but those which are still pathogen free can be protected with certain fungicides. Be SURE to contact your local extension office with your suspicions. They will be able to help you.

Hmmm. I'd suggest sunburn. Any recent hot spells, perhaps within the past month?

I doubt the problem is Phytophthora ramorum, which goes by the name of sudden oak death (SOD) -- but isn't sudden nor is it restricted to oaks.

Suggest you review the facts at the SOD Mortality Workforce at http://www.suddenoakdeath.org/

You can download the symptom card for camellia from http://www.suddenoakdeath.org/html/nursery_photos.html