Eureka, California
"Eureka" received its name from a Greek word meaning "I have found it!" This exuberant statement of successful (or hopeful) gold rush miners is also the official motto of the State of California. Eureka is the only U.S. location to use the same seal as the state for its seal.
Erlking
It has been suggested, that the term may derive not from "elf-king" but from the name of "Herla", a figure in medieval English folklore, adapted as "Herlequin", "Hellequin" in medieval French, in origin the leader of the Wild Hunt, in French known as "maisnie Hellequin" "household of Hellequin" (and as such ultimately identical with Woden), but recast as a generic "devil" in the course of the Middle Ages (and incidentally, in the 16th century also the origin of the Harlequin character). Sometimes also associated is the character of "Herrequin", a ninth-century count of Boulogne of proverbial wickedness.