Terrain analysis of the Racetrack Basin and the sliding rocks of Death Valley

The Racetrack Playa's unusual surface features known as sliding rocks have been the subject of an ongoing debate and several mapping projects for half a century, although the causative mechanism remains unresolved. Clasts ran ging in volume from large pebbles to medium boulders have, unwitnessed, man euvered around the nearly flat dry lake over considerable distances. The co ntroversy has persisted partly because eyewitness accounts of the phenomeno n continue to be lacking, and the earlier mapping missions were limited in method and geographic range. In July 1996, we generated the first complete map of all observed sliding rock trails by submeter differential Global Pos itioning System (DGPS) mapping technology. The resulting map shows 162 slid ing rocks and associated trails to an accuracy of approximately 30 cm. Alth ough anemometer data are not available in the Racetrack wilderness, wind is clearly a catalyst for sliding rock activity; an inferred wind rose was co nstructed from DGPS trail segment data. When the entire trail network is ex amined in plan, some patterns emerge, although other (perhaps expected rela tions) remain elusive: terrain analysis of the surrounding topography demon strates that the length and morphology of trails are more closely related t o where rocks rested at the onset of motion than to any physical attribute of the rocks themselves. Follow-up surveys in May 1998, May 1999, August 19 99, and November 1999 revealed little modification of the July, 1996 slidin g rock configuration. Only four rocks were repositioned during the El Nino winter of 1997-1998, suggesting that activity may not be restricted to wint er storms. (C) 2000 Elsevier Science B.V. All rights reserved.