On a dry lakebed in Death Valley, rocks weighing up to 320 kilograms locomote themselves slightly uphill over time, often leaving zig-zag trails in their wakes. Geologist Paula Messina has painstakingly documented boulder movement via GPS. Smells like a hoax? Take a look at this table, linked to hard data on every named rock. A time-lapse map records boulder movement over time — some have chugged as far as 3.2 kilometers.
The mechanisms for these unusual events have been hypothesized and in some cases tested, but never proven.