Standing outside of the Buckner House in Klamath, a simple-minded fellow named Torr tells you that "bugmen" have been raiding his brahmin at night. Agree to his plea and you'll be sent to where he keeps his livestock.
Kill the radscorpions to finish the quest. You will have to go hunting for them, as they will not come when you are both there. You can also confront the Dunton Brothers who are standing to the west of the shack. If you agree to rustle the brahmin., you can tell them to abort the plan which will cause them to run away (this requires a speech of 50). You'll get the same reward either way.