The stone is native Texas limestone, supplied in this case by Texas Crushed Stone (near Round Rock and Georgetown, Texas). The randon shaped "rubble" rock you see is actually just remnants (leftovers) from the stone quarry operations. The square cut stone is both chopped face and smooth cut faces. This stone is available from most any quarry in the central Texas (Austin) area, several are located in Jarrell, Texas, about 40 minutes north of Austin. The stone is solid masonry individual pieces, approximately 4" to 5" thick. It is placed one stone at a time by very skilled stone masons and anchored in place with masonry mortar.