Beckwith, G.H., Slemmons, D.B., and Weeks, R.E., 1991, Use of low-sun angle photography for identification of subsidence-induced earth fissures, in Johnson, A.I., ed., Land subsidence: Proceedings of the Fourth International Symposium on Land Subsidence, held at Houston, Texas, 12-17 May 1991: International Association of Hydrological Sciences (IAHS) Publication no. 200, p. 261-269.