Under most state and federal laws, animals are considered as property and have little or no legal rights of their own. If you witness an animal being neglected or abused, this is an Animal Control issue and you must contact them immediately, and report the situation. Rescue Organizations can do very little when an animal has a legal owner. However, if animal control confiscates the dog from the owner and takes it to the shelter, a rescue organization or a private party can legally adopt it from the shelter when it becomes available.
For more information regarding animal neglect and laws please visit these websites:
In the state of California animals are considered property. Only animal control can confiscate the dog. Please immediately contact animal control to report this incident. However once the dog is in the shelter then you can adopt it yourself or network the dog to a rescue group.