This is a set of three cards from Oyama Dam in Hita City, Oita Prefecture: a dam card and a geological card. The set includes: ① the standard card Ver. 1.1 (March 2018), ② a commemorative card for the 30th anniversary of the Emperor's reign (February 24, 2019), and ③ a dam geological card, Ver. 1.0 (March 2020), issued by the Japanese Society of Engineering Geology. The geological card features a geological map of the foundation excavation surface of Oyama Dam. Oyama Dam is where a statue of the Attack on Titan manga artist, Hajime Isayama, who is from Hita City, is erected. Keywords: dam, dam card, Emperor's reign, geological card