How common is it? These are some of my family/ancestors from back in the day. 

 

 

According to my mother we have some Mehicano ancestry.

Many AfroAmericans with roots west of the Mississippi River have Mehicano ancestry given the history of Mehico and how far that nation actually reached BEFORE the battle of the Alamo that vastly reduced it's geographical size.

As I said on another thread, most AfroAmericans have varying amounts of Native American ancestry whether it's documented or not.  Most of the Mehicanos we speak of were actually Native Americans racially.