Based on our work we estimate there are 100,000 abandoned mines in the State of Arizona.
Many of the old mines were worked in the late 1800's through the 1940's. When the mines played out, or the market for metals got bad, the miners simply walked away in search of richer finds elsewhere. Even on mines that were patented (sold to the miner by the government) the original owners are long dead. Their descendents often don't know what they own or the mine has been sold for taxes or repossessed by the state.
Arizona Revised Statute §27-318 states: Every mine operator or former mine operator or claimant who owns a mine or mining claim or possess a mine or mining claim under lease, contract, permit or otherwise, who knowingly permits the existence on the premises of an abandoned or inactive mining shaft, portal, pit or other excavation which is dangerous to persons legally on the premises, who fails to cover, fence, fill or otherwise secure it and post warning signs, within sixty days of notification by the inspector and who fails to keep it so protected is guilty of a class 2 misdemeanor. This means that anyone owning a mine must keep it fenced and have warning signs posted. There are no requirements for the type of fence or sign but the following are recommendations based on the standard used in Nevada.