Very early on in my research for the book, one of the most useful resources were the various archives at UT Austin. The Dolph Briscoe Center for American History is a vast source of Texas history. Most relevant to the San Saba story, it holds the papers of J. Frank Dobie, including his file, with correspondence and interview notes, regarding Coronado’s Children. In that same file is the unpublished manuscript that William Longworth wrote. Another archive at UT Austin is the Harry Ranson Center, and material from there turned out to be useful as well.
A search of the Dolph Briscoe website indicated that there might be some useful materials there, but I was living far away from Austin at the time. So I engaged the services of a professional researcher. I think I was lucky to have found a good one. His name is Ralph Elder. He was very familiar with the various archives at UT Austin and I think he went on three research visits in total. For the first search he went above and beyond what I asked for, and he found some fascinating material. If anyone is interested in using him to locate and photograph materials at the various archives at UT Austin, he can be reached at Ralph.L.Elder@gmail.com .