The Monstead Tunnels in Joshua Tree National Park aren't any kind of secret, they're just not listed on any maps. Nor are they listed in any of the hiking guidebooks for J Tree. There is scant information to be found regarding their years of operation or production. Nothing much of historical significance is left on site and the tunnel openings have been "bat-gated" by the NPS for safety reasons. If you asked a Ranger about them, he'd probably reply, "what?" So why on earth would anyone even bother hiking a couple miles to visit them?