Unfortunately there are no recent/accurate USDA zone maps for Mexico that I know of (the latest one I have was made in 1984). If you end up finding one, please let me know!
Wikipedia tells me that it can get down to "0 degrees C or lower, with frosts" in the winter in Guanajuato ... which sounds like USDA zone 10. But your city or neighborhood may get colder or less cold in the winter -- it's best to take readings for yourself if you want to do any serious gardening.
If I were you, I would contact your local agricultural office for more specific information -- they can be extremely helpful, especially for information on plants which do well in your area.