S. Nuraini, “FENOMENA HARD GROUND PADA BATU LEMPUNG KAYA GAMPINGAN FORMASI NANGGULAN, DI SUNGAI WATUPURU, PEGUNUNGAN KULON PROGO, YOGYAKARTA”, Journal Technology of Civil, Electrical, Mechanical, Geology, Mining, and Urban Design, vol. 4, no. 1, pp. 95-102, Jun. 2019.