I'm So Glad to find your message. I have been searching for years to find any reference to Nitre Mining in TX. I have a copy of my G Grandfather's Pension Application & it says he was a Guard at the Nitre mine above Uvalde. It gives no info as to the Company he was with etc.
It must have been a closely guarded secret even to this day. I tried to get info from the National Archives but no luck. He thought two of the officers were Gen Knox & Lt Reed; he was in the Infantry & served from Spring of 1863 to Spring of 1865. His name was Wm Friday.
Thanks for any help.