Mt diablo a general policy (which might require a bit of interpretation), "Dogs are allowed only in developed areas of the park. They must be kept on a leash during the day and in an enclosed vehicle or tent at night. Dogs are NOT permitted on trails, fire roads or in park buildings."
Dogs are only allowed on paved areas or within the campsites. Dogs are not allowed on trails or dirt roads. They must be on a leash at all times. Its a big tease for Dogs. I'd recommend NOT bringing your pets to Mount Diablo.
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