Abstract: A post anchor/anchor adapter system is unitary cast or machined steel or the like. An anchor/ adaptor alone is driven alone into a hole cut in in-place concrete. The system includes an anchor extension tube for driving into soft soil. The inventive anchor/adaptor has a body in the form of an elongate square tube having radius-curved corners vertically driven into a round receiving hole, forming creases and a secure anchor. The tube has an upper female portion for a post and a lower female portion for an extender and is divided by a horizontal plug wall integral with the tube structure. The lower female portion of the anchor/adapter tapers outward towards its lower open end allowing for an interference fit with the driven tube acting as an anchor. The female portion upper end has crescent-shaped tabs defining a disk sized to plug the drilled hole.