It looks to me as if your problem is cracking rather than critter damage.

Tomatoes crack primarily because of inconsistent moisture (the inside of the tomato grows quicker than the skin can stretch). Temperature changes can also play a role.

Some tomato varieties are more prone than others to cracking. For instance, my Black Krims crack horribly! (But the taste is worth it.) On the other hand, just next to my Black Krim is a Rutgers: lovely fat tomatoes, the vast majority without any cracks at all.

There are three types of cracks: radial cracks (which begin at the stem and radiate outward; these can be very deep); concentric cracks (these form circles or semi-circles around the stem -- your photo shows a concentric crack); and spiral cracks (which spiral around the fruit irregularly; some tomatoes crack so badly they burst).

In hot sun, some tomatoes have tiny cracks on their shoulders: this is called shoulder checking and is variety-related.

The split at the bottom of your tomato is not typical (though I have a cherry tomato that likes to split across the bottom like that). The split in your picture is also unusually wide -- but it doesn't look like caterpillar damage, and it looks much more like a crack than any type of animal damage. Have you had a lot of rain (probably not, as you're in California), or did you give your plants more water than usual recently?

There are some things you can do to limit or prevent cracking. One is to mulch around and under your tomato plants: that lowers the amount of water that evaporates from the soil, so your plants will be less likely to dry out between waterings. Another is to water regularly (and at least 1" per week -- but not too much, or the flavor of the fruit will suffer!). And you can buy tomato varieties that are less prone to cracking; here's a list:
http://www.harvestwizard.com/2009/07/crack-resistant_tomato_varieti.html

It's been a dry summer here. We had three or four days of certain rain headed our way. Yesterday I picked every tomato that was showing a significant amount of yellow. If I hadn't, they would have been guaranteed to crack because of the multiple inches of rain we're getting.