From Guild of Archivists

The Amad were a Native American tribe in the American southwest. Gehn believed that they were related to the D'ni in some way due to their possession of advanced technology. His wife, Keta, was Amad.

It is possible that Gehn's belief that the Amad were related to the D'ni was not unfounded. Shortly after the D'ni arrived on Earth, they undertook a project to expand the network of natural tunnels which supplied fresh air to the D'ni cavern. Several workers went missing near the conclusion of this effort, and were believed to have remained on the surface. They may have married into the local native population and brought some of the D'ni's technology with them.