There are as many good/experienced tortoise keepers who believe that hibernation is not a necessity but an adaptation. If the weather is conducive to hibernation then it probably is best to let the animal do what comes natural but if the temperatures remain in the upper ranges to where the animal is not inclined to hibernate, I don't think it does any harm to let it do its thing. There are many Desert Tortoises in SoCal that provide proof of this line of thought. I'm talking about the hundreds of backyard DTs that have been kept over the years by people who 'don't have a clue' as to what they are doing. (btw, it is these people I have the greatest respect because they admit they don't have a clue and listed to what their pets tell them)(the best kind of keeper in my opinion).
I've got a pair of Hermans (eastern form) that do not hibernate. (i'm in San Diego) They do slow down but move about during the warmer part of the day.
If you (the person in San Diego) are inclined to hibernate your animal for the purpose of, say, inducing breeding behavior you can accomplish this naturally by providing a dry, insullated area to where the daytime highs are not experienced. This can be risky because you take controll away from the animal.
Anytime you take control away from the animal you are adding risk.
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Ed
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Trying to keep the fun in Chelonian care