The Baigong Pipes are found on almost any list of "Out of Place Artifacts" — anachronistic objects that seem to defy explanation.
Local legend speculates that Mt. Baigong in the Qinghai Province of China is an ancient extraterrestrial laboratory. Aside from the mysterious pyramid that crowns the mountain, three triangular entrances at the mountain’s base lead the way to hundreds of decrepit metal pipe-like structures of unknown origin.
The rusty tubes, ranging from needle-size to 16 inches in diameter, reach from deep inside the mountain to a saltwater lake 260 feet away. Many of the hollow pipes are uniform in size and seem to be placed purposefully. The ancient objects are embedded deep enough into the mountain wall and floor to preclude modern human handling. The inhospitable environment surrounding the mountain sees only the occasional nomad. Unless these wanderers developed secret advanced metallurgy skills, the pipes were not formed by human hands.
The first scientists to examine the subterranean phenomenon concluded that the pipes were composed of 92% common minerals and metals and 8% unknown materials. The obvious inference is that these red-hued tubes were transported here from outer space as part of an alien public works project. This Martian theory has garnered so much support that a monument topped off with a corroded satellite dish has been erected near the mountain.
The most recent researchers to examine the pipes believe that the metallic phenomena are in fact fossilized tree root casts, the rusted tubes being the result of tree roots that underwent the processes of pedogenesis (the process that forms soils) and diagenesis (transformation of soil into rock). Further experiments confirmed that the pipes contain organic plant material and even microscopic tree rings. Overflow from an extinct lake once carried these roots to where they stand now.
So while they aren't part of an alien sewer system, the pipes are evidence of the Earth’s ability to create strange and remarkable objects.