Noun
highwall (plural highwalls)
(mining) The unexcavated face of exposed overburden and coal in a surface mine.
Highwall mining can produce thousands of tons of coal in contour-strip operations with narrow benches, previously mined areas, trench mine applications and steep-dip seams with controlled water-inflow pump system and/or a gas (inert) venting system. Source: Internet
Highwall mining Caterpillar Highwall Miner HW300 - Technology Bridging Underground and Open Pit Mining Highwall mining is another form of surface mining that evolved from auger mining. Source: Internet