There is nothing at the posted coordinates, but this is the entrance to Camp Mabry. There is nothing placed within the entrance area or the boundaries of Camp Mabry.
This cache can only be found after completing the Texas Military Forces Museum Adventure Cache. Once you complete each stage of the Adventure Cache, check the journal entries for bonus information. Coordinates are in the form N 30 AB.CDE W 097 PQ.RST.
Check the Adventure Cache for access instructions and hours.