Upon arriving in Klamath, head over to the Buckner House and speak with Ardin. When asked what is bothering her, she speaks of her fiancé, Smiley, who has gone missing, with his last known location allegedly being the toxic caves. Agree to keep an eye out for her fiance, and she will mark the location on the Pip-Boy map.
Rubber boots are recommended for getting through the caves without being irradiated. There are numerous geckos of different variations running about that can either be fought, or avoided. Smiley can be located on the 2nd floor of a facility deep inside of the caves, and will be seen hiding inside of a generator room. Talk to him and bring him to the entrance of the caves, where he will give his thanks and leave the party. Afterwards, head back to Klamath in order to receive a reward from Ardin.