Principal formats (within each there are sub-formats or flavors)
1. Regional Mexican.
The country music of México which includes genres like norteña (accordion), banda (tuba and brass), ranchera (mariachi) and lesser varieties. Today, these stations are very current based with high rotations. This format will have much more limited appeal to non-Mexicans, although those from Guatemala, El Salvador and Honduras will definitely listen. It's the biggest format in Spanish, and is on about half of all Spanish language stations in the US.
2. Contemporary.
This is somewhere between CHR and Hot AC in general market equivalency. Mostly current based, today the format is based on reggaetón and rhythmic music, with fewer pop and ballad songs than ever. Rotations tend to be like English language Hot AC. Stations in the Eastern US will be more Caribbean flavored than those in the Southwest, but the biggest hits will be universal.
3. Adult Hits
This is a format that works only in mostly Mexican heritage markets, and is a blend of mass appeal adult pop, softer regional Mexican and some traditional rhythmic sounds. It's a 30-54 format, with no currents, perhaps some older recurrents, and slow rotation gold.
4. Pure Rhythmi
A format variation of #2, but with no pop and no ballads. Often will play some English music, such as Pitbull and Drake. Only seen in a few markets like LA and Miami.
5. All ranchera
Traditional mariachi music. This appeals to an old audience, and would usually be seen on an AM such as KFWB in Los Angeles.
6. Tropical
I list this only because there are almost no examples of pure tropical stations in the mainland US any more. Salsa is almost entirely an older demo (45 and over) format, and Mexican tropical, including a genre known as "sonidero", is pretty dead. Some contemporary tropical may be found on the more Caribbean leaning contemporary stations, but, again, not in the Southwest.
7. Rock en español.
There has only ever been one successful all-Spanish-rock station in the world, and it is in Argentina. A non-starter in the US, even for specialty shows.