If the ground has opened, if a hole is swallowing water or soil, if a wall or a floor has moved suddenly, or if anyone could fall in, call 911 first. A subsidence hole can keep opening, and the edge of it is not safe to stand on.
When nobody is in immediate danger, Arizona State Mine Inspector, Abandoned Mines is the office to call in Arizona. The office that inventories and secures abandoned mine openings and takes reports of them.
Then tell the people who need the record of it: your insurer, your county emergency management office, and, if the hole is in a road or a right of way, the authority that maintains it. Photograph it with something in the frame for scale, write down the date and the time, and keep measuring it, because how fast it grows is what an engineer will ask about first.
Signs worth reporting before anything opens: doors and windows that stop closing, new cracks that run at an angle across a wall, a floor or a drive that dips, a sudden wet patch or a dry well, and a smell of sulphur or a warm patch of ground where snow melts first.