There were two routes to cross Texas for those traveling to the 1849 gold rush. One of them crossed the San Saba River near the old Spanish presidio. One of the earliest records of the abandoned presidio and various rumors of the mine were in the Huff Diary. That a route to the California gold rush went past the old presidio may be very important in unraveling the larger treasure legend.
The diary can be read here. There was some controversy about the diary when it was discovered and made public some years ago. An article by one of the people who first examined the dairy is here. My impression is that the diary was written by William Huff, but it was probably a final draft written after the gold rush, based on notes taken during the trip. First draft, final draft, does it really matter?
There was a map to the mine in the diary, but it is useless, something like a random X next to the river. Of much more interest was what Huff wrote about what Jim Bowie told him about the mine and what a couple of Tejanos told him about their experiences at a mine north of San Antonio when they were children.
In celebration of the diary, in 2005 some school kids retraced the wagon train route. It appears that despite the controversy with the diary that a fun time was had by all in the end.