Copperhead
Copperhead is a prominent massif in the Ramtops above Lancre. The mountain is big but is still small enough to be big enough to have a name, unlike really big mountains.
Copperhead is settled by several dwarf clans and possibly trolls as well. Dwarfs from Copperhead were the first to migrate to Ankh-Morpork.
Copperhead dwarves have a reputation for being much more friendly to humans and trolls than the more conservative clans mining below Überwald (the Deep-Downers), having had to deal with humans from Lancre in trade for many years, and Ankh-Morpork more recently. In Copperhead you can find excellent dwarf thudmeisters, which surely also contributes to the open attitude of the Copperhead dwarves.
Annotations
The name may be an allusion to the mountain Caradhras in Tolkien's Lord of the Rings, whose name translates roughly as "Ruddyhorn" or "Coppery-peak." In the Roundworld, a "copperhead" is a venomous snake (Agkistrodon contortrix) native to eastern North America.