There's a website called the 10,000 year clock. It explains in detail the project to put a clock inside the Sierra Diablo Mountain Range that will last for 10,000 years. In fact, if you want even more detail, check out this site, where there's a very long post about the clock - and others like it.
Reading through the post on Technium, I had to keep asking myself if this was all some sort of hoax. The explanation for trying to create a clock that will last (of its own accord) for ten millenia is related to people who think long term rather than short.
The clock's inventor, Danny Hillis, wrote: I cannot imagine the future, but I care about it. I know I am a part of a story that starts long before I can remember and continues long beyond when anyone will remember me. I sense that I am alive at a time of important change, and I feel a responsibility to make sure that the change comes out well. I plant my acorns knowing that I will never live to harvest the oaks.
I want to build a clock that ticks once a year. The century hand advances once every 100 years, and the cuckoo comes out on the millennium. I want the cuckoo to come out every millennium for the next 10,000 years.
The photo shows one of the models relating to the clock.