I think what you're looking for is called a "Range". There are many of them throughout the state. Some of them are even outdoors.
Just because an area isn't "Posted" doesn't mean its open to the public. You may sometimes get away with walking on someone's private property if you're looking for your dog that slipped off his leash or your child that wandered away from the family picnic at the nearby public park. It is NOT "OK" to just shoot on a piece of land because there aren't signs that say you can't.