The Gilman Tunnels were a part of the former Santa Fe Northwestern Railway, which operated a logging route in the Jemez Mountains 1924-1941. Logging operations continued by truck until 1973. The land is now part of the Santa Fe National Forest. The stone it passes through has been radiometrically dated to 1.45 billion years old - a Precambrian monzogranite. The tunnels sit almost exactly on the Jemez-San Ysidro fault line, and you can see the slip just after the second tunnel.
