I earned my private pilot's license while living in San Diego. My cross country flight in a Cessna 150 started at Brown Field (next to the Mexican border, 5 miles inland from the coast). The first stop was at Twenty-nine Palms. I refueled there and flew to Yuma, AZ for the next leg. The third leg was Yuma, AZ back Brown Field. Each leg was required to be over 100 miles. The Piper referenced in the story would have a range of 100+ miles on a single tank.
Mexicali/Calexico is south of El Centro. There are small airstrips all over the desert. I frequently stopped at the Imperial strip. There are many places to re-fuel, so the max range on a tank of gas is not a limiting factor.
SlowBoat, here is a spec sheet:
http://www.risingup.com/planespecs/info/airplane447.shtml
Here is info on all Piper aircraft. There seems to be more than one type of Piper Pawnee 25.
What can be added to fuel that would create a problem for the plane?
Would water added to the fuel create a problem?