Bodie State Historic Park
A genuine Californian gold-mining ghost town, Bodie officially became the Bodie State Historic Park in 1962. It is recognized as both a National Historic Landmark and a California Historical Landmark. From what I've read online, it's generally considered to be the best ghost town in California.
Only a small part of the town remains, but at 170 buildings small is relative. It's preserved in a state of "arrested decay," which basically means the State is preventing the structures from falling down or otherwise deteriorate in a massive way. It would appear that as part of this "arrested decay" preservation, pretty much all the buildings have been sealed off meaning you can enjoy walking through the town, but not inside the buildings with few exceptions.
In comparison, when I visited the truly unique ghost town of Kolmanskop, Namibia, you could freely go inside the buildings although that was under the "enter at your own risk" disclaimers. Often times that meant going in through the windows, which made it all that much more exciting. Realistically though, Kolmanskop doesn't get that many visitors compared to the 200,000 per year that Bodie gets.
While you can't quite roam the buildings freely like you can in Namibia, this ghost town is still worth a visit with plenty to see and enjoy. Especially if you've never been to a ghost town before, it's quite enjoyable and family friendly.
A number of the remaining buildings in Bodie.