This was a common sight in the fifties, yet no one fell into the open shafts.  The derrick was often dismantled and the shaft was simply left as is.  Of course, there were no dune buggies nor motorcycles speeding around then, either.  This picture shows the "cribbing".  The shafts were lined with timbers, usually down to the solid rock, to keep the sides from crumbling into the hole.  Usually, it extended above ground, to prevent rain water from running in.  This particular shaft, at one time, had concrete "curbing" which is mostly gone.
Notice the car on the highway in the background.