The Barberton Greenstone Belt
There are a lot of really old mountain ranges in the world (Appalachians represent!), but the Barberton greenstone belt in South Africa has got them all beat. This bunch of monolithic rocks started edging out of the ancient sea floor 3.5 billion years ago. The Earth had barely even gotten its life together when these mountains showed up! Naturally, they are packed with amazing scientific specimens, and a whole lotta gold.