From The Vault
The Toxic Caves are north of Klamath. Before the war it was a military warehouse of some sort. Now it's a radioactive cave inhabited by Geckos (little and gold, though mostly gold). Some good equipment can be found here provided that you have a set of Electronic Lockpicks and some repair skills. Be ware of the security robot that resides here, who will attack with rocket launchers as soon as you go down the elevator. Strangely, the Electronic Lockpick Mk II doesn't work for this. Also Smiley, the trapper from Klamath, is waiting there for you to save him.
Ardin Buckner will put the Toxic Caves on your map when you get the Save Smiley from toxic caves quest.