Back across the border into California, about 15 miles West of Yuma are the Imperial Sand Dunes, aka Algodones Dunes, which run about 45 miles long. The Historic Plank Road ran across these dunes before paved roads.

The Imperial Sand Dunes as seen by Google Earth.
You can read about them by clicking these three links…
http://en.wikipedia.org/wiki/Algodones_Dunes
http://www.blm.gov/ca/st/en/fo/elcentro/recreation/ohvs/isdra.html
http://www.desertusa.com/sandhills/plankrd.html
All original material Copyright – Jim Jaillet 2009
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http://www.panamaorbust.com