In Guatemala the currency used is the Quetzal which has a value of approximately $2.5pesos = 1Quetzal. Or $1USD = 7.5Q.
In most places USD are also accepted as readily as the national currency, although don’t expect the exchange rate to be great. There are plenty of exchange businesses during the trip (except in Tikal), and even though the airport gives a bad exchange rate, you can purchase Quetzals upon arrival in Guatemala City.