Who the tar?

WHO THE TAR? -- "White envelopes containing $10 bills have been arriving anonymously in the mailboxes of residents of a small south-central Kansas town.
The mystery has confused and delighted residents of Turon, pop. 436. 'My first thought was that I had a birthday recently,' said Markoleta Padgett, who found her envelope last week. 'But I thought, 'Who the tar would send me something for my birthday and not put a name on it?' "

Is this a version of "who in tarnation"?

That's my guess.