Mongols MC isn't a Mexican gang. They're traditionally the MC which attracts the most Mexican American bikers and granted over half of the Mongols members in Cali do probably have Mexican heritage, but there are lots and lots of white Anglo Mongols members (including chapter presidents) as well.
In California there are plenty of Mexican American Hells Angels as well. In Texas there are tons of Mexican Americans in the Bandidos.

Outlaw motorcycle membership in the American Southwest is largely a mix of Anglo Americans and Mexican Americans. It's not unthinkable there are cartel connections making rounds in those clubs, but we can't say for sure. At the end of the day, these are all American clubs first and foremost.