What in Tarnation !?

tarnation

SYLLABICATION: tar·na·tion
PRONUNCIATION:
tär-nay-shun
NOUN: New England & Southern U.S. The act of damning or the condition of being damned.
INTERJECTION: Used to express anger or annoyance.
ETYMOLOGY: tarn(al) + (damn)ation.
REGIONAL NOTE: The noun and interjection tarnation illustrate suffixation, the addition of a suffix to a word. Tarnation and darnation (the latter probably having come first) are both euphemistic forms of damnation. Tarnation seems to have been influenced by tarnal, another mild oath derived from (e)ternal! The Oxford English Dictionary cites late-18th-century examples of tarnation from New England, indicating that it has been part of American speech since colonial days.

I always wondered where the word tarnation came from and what exactly it meant. I cant ever say the word without getting a visual of Yosemite Sam. Same goes for the word Varmint.