Don't know where Mamoth Wash is, but Mammoth Wash is at the start of the dunes!
Really wasn't my SB The Dunes run North to south and have been blowing south east for thousands of years and started close to the Salton Sea and stretch all the way into the Sonora Desert in Baja and mainland Mexico! Mammoth Wash is the oldest part of the Imperial Dunes on their never ending mach!