The Butajiri-Silti volcanic field consists of a large group of basaltic cinder cones, maars, and lava flows in an 80-km-long, NE-SW-trending area near the west margin of the Ethiopian Rift. At least 13 maars, many filled by lakes, are located near the town of Debre Zeit, SE of the capital city of Addis Ababa. The maars were erupted through Pleistocene rhyolitic lava flows and tuffs. Eruptions of the younger basaltic cinder cones were contemporaneous with those that produced the maars. Some of the lava flows associated with the cinder cones are very young and are considered to be prehistorical in age (Di Paola, 1972).