Have you checked -- isn't there an Owens Valley bus that will take you from Lone Pine to Mammoth or Lee Vining?
Crest, now ESTA -- Eastern Sierra Transit Authority, northbound bus leaves Lone Pine at 6:15 AM every day, goes all the way to Reno.
Thanks Steve C. for the reply. I was told by ESTA that they do not run buses on the weekend and since July 31 is a Saturday I figured we needed another form of transport to Mammoth. Is this still true?