There are roughly a kajillion hiking groups online based in California, a lot of them on meet up, some not.

You'll find that a lot of them are based in LA. Though you won't be able to take the dog on any of the national park hikes, and some of the state park hikes, you should be able to find plenty of national forest outings with groups.
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"In the beginner's mind there are many possibilities. In the expert's mind there are few." Shunryu Suzuki

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