Units who lost prisoners in this area were as follows:
20th Iowa, December 1863 and March 1864 Aransas Bay
13th Maine, December 1863, Aransas Pass
22nd Iowa, February 1864, Indianola
21st Iowa, 22nd, Iowa, 23rd Iowa, 99th Illinois - Jan-Feb. 1864, Lavaca, Texas.

Books and References:
History of the Thirteenth Maine Regiment, Bridgton, ME, (Clark W. Bryan And Co.)
The Story of the Maine Fifteenth, Bridfton, Me.(THe Bridgton News)1890
See also
Malsch, Brownson, Indianola - The Mother of Western Texas. (Austin, Shoal Creek Publishers, 1977)
Briscoe, Eugenia Reynolds ,City by the Sea - A History of Corpus Christi, Texas, 1519-1875 (New York, Vantage Press, 1985)

If you will do an Official Records Search, look for "Powderhorn" as that was a period place name that is often referenced.
Hope this helped.