Jesse Stone wrote IDAHO. It's mostly known as a jazz standard, but there have been crossovers into western swing. It's sometimes sung, sometimes done as an instrumental. Jethro Burns did a nice version on mandolin.

I don't know if the following lyrics are complete, but they're all I can find:

No worry on my mind,
It's peace that I find
Away beyond the hills in Idaho,
Where yawning canyons greet the sun
As it smiles above the trees in Idaho
To say another night is done.

Warm summer winds toss the waving grain
Calling me back to my home again
To dream sweet memories of long ago
Beyond the hills in Idaho.

The Online 78rpm Discographical Project lists the following early recordings:
Alvino Rey & His Orchestra, 9/19/41
Merry Macs, 2/21/42
Guy Lombardo's Royal Canadians, 6/2/42
Benny Goodman & His Orchestra (v. Dick Haymes), 6/17/42
John Hardee Swingtet, 2/28/46
Gene Ammons Sextet, 6/19/47
Ray Anthony & His Orchestra, n.d.
Hilton Jefferson, n.d.
Leroy Holmes & His Orchestra, n.d.
Les Hite & His Orchestra, n.d.

(More or less as I suspected, it's canyons that yawn, not mountains.)