1. 20,000 Kilometers Over Death Valley: The GPS View of the Sliding Rocks Paula Messina Geology Department San José State University

3. Racetrack Playa: Physical Setting +1131 meters ~4 km. (north-south); ~2 km. (east-west) Surface: sand, silt, clay; desiccation polygons

4. February, 2001: Seven Inches of Snow

6. Grandstand Racetrack Road Ditch Ponding Water September, 1997

7. Sliding Rocks

8. Why Do Rocks Slide? Ice rafting? Wind alone?

9. What is the Complete Network? Does non- parallelism among trails imply wind alone? How can all the trails be mapped?

10. Does a Rock’s Character Contribute to its Activity? Do rounder rocks inscribe more- sinuous trails? Do larger (more massive) rocks produce shorter trails?

11. Global Positioning System to the Rescue 24 satellites 20,000 km. (12,000 mile) orbits 24 hour global coverage Sub-meter accuracy Full operational capability: April 1995

12. How Does GPS Work?

13. Mapping Mission July 16 - 23, 1996 162 rocks/trails Two field mappers Human “digitizers” walked over 100 km.

14. Cartographic Entities Points Lines Areas

15. In-field Data Download Post-processed differential correction Export to ArcView GIS Shape File format Export to MS Excel for Quantitative Analyses

16. Final Map Predominant motion: SW-NE (slightly uphill) Trail length  f (rock size) Trail straightness  f (rock shape) Parallelism is the exception; not the rule. Inferred Wind Rose

17. Plots Showed No Statistically- Significant Correlations

18. Trail length appeared spatially controlled –(see following slides) What Factors Control A Rock’s Ultimate Distance Traveled? Image and trail map for Diane, the rock that inscribed the longest trail

23. What Factors Affect Trail Straightness? Straightness= Total Trail Length Start  End Distance

24. Trail straightness appeared spatially controlled What Factors Control A Rock’s Ultimate Path? Crooked trails Straight trails

25. What Factors Control A Rock’s Ultimate Path? GIS-Generated Aspect Map

26. Intervisibility: Ray Tracing Cross-section: Map View:

27. Intervisibility Maps for Representative Rocks

28. Trail Character Correlates to Surrounding Terrain

29. The Racetrack: A Mosaic of Microclimates Wind tunnels Turbulence

30. The Final Word: How Can Rocks Converge?

31. More Information on the Sliding Rocks: Paula Messina’s Racetrack Web Site Smithsonian magazine: July, 1999 California Geology: January, 2001 “Savage Planet” Episode IV: “Extremes” Discovery Channel Online’s Dancing Rocks Web Site