36.6667°N, 117.5667°W.
Geological phenomenon at Racetrack Playa, Death Valley National Park, California, where dolomite stones up to 320 kg leave linear tracks across the dry lakebed sediment without any documented agent moving them. Tracks are typically a few millimetres deep and run for tens to hundreds of metres, sometimes turning sharply or running parallel to neighboring stones. The mechanism remained unsolved from first scientific attention in 1915 until December 2013, when Richard Norris and James Norris (Scripps Institution of Oceanography) captured the motion on time-lapse cameras. The mechanism: rare combinations of rainfall (3–5 cm), overnight freezing forming thin floating ice panels, and light morning winds (3–5 m/s) push the brittle ice sheets across the lubricated mud, dragging the embedded stones at speeds of 2–6 m per minute. The phenomenon was finally recorded after 98 years of speculation.
Stones that move themselves on a desert floor were finally caught in 2013 — by ice that drifts only when nobody is looking.