[2] Based on a story by Karl Brown, the film is about a singing cowboy and rodeo champion who inherits a ranch and mining property along with his foster father's niece.

The other half is left to Dad's niece, Barbara Erwin (Carol Hughes) who arrives at the ranch from the East with her friend, Kitty Callahan (Pauline Drake).

Gene, however, wants to continue Dad's work on the mine, which employs Mexican rancheros whose land was ruined by dust storms.

Back at the ranch, Gene grows frustrated with Barbara and Kitty who have drawn a line down the middle of Dad's house—dividing it exactly in half.

Soon after Gene rides off, Dad's lawyer arrives and expresses concern when he learns about Barbara's dealings with Arnold and Fry.

Afterwards at a fiesta, Gene sings a beautiful song to Barbara and romances her, Frog and Kitty share loving glances, and even Tadpole changes his mind about women and goes off with a pretty señorita.

Under Fiesta Stars was the third Gene Autry film featuring leading lady Carol Hughes, preceded by Gold Mine in the Sky (1938) and Man from Music Mountain (1938).

After appearing in stock and vaudeville for several years, she began her film career in 1935 playing bit parts and supporting roles.