According to findagrave.com, it is unknown.
http://www.findagrave.com/cgi-bin/fg.cgi?page=gr&GRid=45114623
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It was in an unmarked grave. Clint Eastwood's character "Blondie" said he was writing the name of the grave on the bottom of a rock, then, after the three way shoot out it was revealed to Tuco that there was no name on the rock, because the gold was buried in an unmarked grave. When the gold was found the grave marker was simply a piece of unmarked wood.
Some where
with a X
tombstone
Trenches - 2010 Shallow Grave 1-5 was released on: USA: 22 February 2010