Simplify the following text for a Grade 13 native English-speaking person.
Original: The Maya calendar is a system of calendars and almanacs used in the Maya civilization of pre-Columbian Mesoamerica , and in some modern Maya communities in highland Guatemala and Oaxaca , Mexico .
Simplified: The Maya calendar is a system of calendars and almanacs used in the Maya civilization of pre-Columbian Mesoamerica , and in some modern Maya communities in highland Guatemala .