Earth fissures are one of the geologic hazards that have damaged the facilities of the Central Arizona Project (CAP). Earth fissures exist along at least two reaches of the Tucson aqueduct, and more are likely to develop in the future. Within the region investigated for this project, potential hazards resulting from earth-fissure development were recognized during the CAP-planning phase and the proposed route of the aqueduct was changed accordingly (Schumann and others, 1984). Where the aqueduct had to pass through a zone of existing or potential fissures, its lining was strengthened with reinforcing steel mats (Sandoval and Bartlett, 1991). The lining was tested when an earth fissure developed beneath the aqueduct in Avra Valley during 1988, in a previously identified hazard zone (Anderson, 1988). The steel mats successfully supported the aqueduct (while it was full of water) until repairs were completed. Through careful planning, construction, monitoring, maintenance, and repair, the U.S. Bureau of Reclamation (USBR) has been able to minimize the impact of fissures on the CAP.