Highwalls are vertical cliffs. They are common features of open pit mines and quarries which can be unstable and prone to collapse. Do not stand near or under highwalls nor attempt to climb them. Mines are not caves. Caves are formed naturally over thousands or even millions of years.
Mines are man-made by blasting, which fractures and weakens the surrounding rocks.
Vibrations from walking or even speaking can cause an abandoned mine to cave in. Abandoned mines are not ventilated. Consequently, pockets of deadly air and gases can be present. Even experienced cavers can die exploring mines, due to lack of oxygen. Structures are dilapidated.