As of December 31, 2015, we operated two mining complexes located in Central Appalachia (Tug River and Rob Fork), along with our Elk Horn coal leasing operations in Central Appalachia. In December 2015, we completed the sale of our Central Appalachia Deane mining complex to a third party. In August 2016, we completed the sale of our Elk Horn coal leasing company to a third party.
As of December 31, 2015, we operated two mining complexes located in Northern Appalachia (Hopedale and Sands Hill) and one mine located in the Western Bituminous region in Utah (Castle Valley). During 2014, we developed a new mining complex in the Illinois Basin, our Riveredge mine at our Pennyrile mining complex, which began production in mid-2014. The Pennyrile complex consists of one underground mine, a preparation plant and river loadout facility.
We define a mining complex as a central location for processing raw coal and loading coal into railroad cars or trucks for shipment to customers. These mining complexes include seven active preparation plants and/or loadouts, each of which receive, blend, process and ship coal that is produced from one or more of our active surface and underground mines. All of our preparation plants are modern plants that have both coarse and fine coal cleaning circuits.
Our surface mines include area mining and contour mining. These operations use truck and wheel loader equipment fleets along with large production tractors and shovels. Our underground mines utilize the room and pillar mining method. These operations generally consist of one or more single or dual continuous miner sections which are made up of the continuous miner, shuttle cars, roof bolters, feeder and other support equipment. We currently own most of the equipment utilized in our mining operations. We employ preventive maintenance and rebuild programs to ensure that our equipment is modern and well-maintained. The rebuild programs are performed either by an on-site shop or by third-party manufacturers. The mobile equipment utilized at our mining operations is scheduled for replacement on an on-going basis with new, more efficient units according to a predetermined schedule.