Format: Ranchera / Mariachi
Ranchera music originated in the central area of Mexico whose largest city is Guadalajara in the state of Jalisco. Ranchera music today is almost always accompanied by a mariachi thus making the two terms often used interchangeably. In fact, ranchera music is played by a mariachi.
For a detailed explanation of the origins and characteristics of the mariachi,
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While this format was fairly common in the 70's through the 90's, few remain today. The most significant one is KHJ in Los Angeles, known as La Ranchera 930.
Pedro Infante and Jorge Negrete, both fine actors and both excellent singers of ranchera songs.
Ranchera music samples
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Ranchera A format based on ranchera and mariachi songs, usually covering many decades of music, sometimes back to the 50's. Because it appeals to older listeners it is almost always an AM format.
Pedro Infante - Flor sin retoño
Antonio Aguilar - Triste Recuerdo
Antonio Aguilar - Arboles de la barranca

José Alfredo Jiménez - Te solté la rienda
Rocío Dúrcal - La guirnalda
Javier Solis - Sombras
Vicente Fernández - La ley del monte
Vicente Fernández - Miedo
Vicente Fernández - Por tu maldito amor
Vicente Fernández - Volver, Volver

José Alfredo Jiménez - Te solté la rienda
Juan Gabriel - Por qué me haces llorar
Mariachi Vargas de Tecalitlán - Camino Real de Colima
Mariachi Vargas de Tecalitlán - La Adelita
Mariachi Vargas de Tecalitlán - El Carretero
Mariachi Vargas de Tecalitlán - Las Chapanecas

The few remaining ranchera stations also include some norteña music such as these samples.

Los Tigres del Norte - La mesa del rincón
Los Tigres del Norte - La jaula de oro

Ramón Ayala - Tragos Amargos
Carlos y José - El chubasco
Cardenales de Nuevo León - Se renta
Conjunto Primavera - Ave Cautiva
Los Tiranos del Norte - Hasta la miel amarga

Los Rieleros del Norte - Ni el Diablo te va a querer