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I, feature in the project area. As shown on Figure D. t-1, the main line of the Sangre de Cristo Fault trends north-south at the edge of the foothills, approximately 2.5 miles west of the proposed mine pits and one mile west of the proposed heap leach facilities. Numerous smaller faults have been associated with the fault system in the project area. As many as 16 smaller faults in this area have been field surveyed by Kirkham and Rodgers. t Kirkham and Rodgers obtained carbon sanples from the banks of the Rito Seco to date recent movement in the area. Their interpretation was that the recurrence interval for fault movement in the area of the Rito Seco was approximately 3,000 to 5,000 years for significant surface rupture and major earthquakes. The last fault rupture occurred during the Holocene Period approximately 1,940 to 4,715 years ago. The ifi th f l d ti d C i F lt i ve ere ore, c ass e as an ac Sangre e r sto au s, fault as defined by Slemmons and McKinney 11977}. However, ' seismic activity has been virtually absent in the San Luis Valley over the 110 years of earthquake recording history. `~ The maximum credible earthquake (MCE) for the project area has been estimated by a number of researchers. Kirkham ' and Rodgers (1981) estimated the MCE for the Southern Rio Grande Subprovince at a Richter Magnitude (M) of 6.5 to 7.5. Algermissen et al (1982) have determined a similar range for the zone surrounding the site of 6.1 to 7.3 M. Glass {1988) ' has concluded that the MCE in the immediate area of the San Luis Project is 6.8 to 7.0 M. Copies of Dr. Glass' reports are included in Appendix B. ' The peak horizontal bedrock acceleration associated with the MCE has been estimated by Glass (1988) to be 60 to 70 percent of gravity (0.60 to 0.70 g). The probability of this peak bedrock acceleration occurring in the next 100 years has been determined by Dr. Glass to be between 0.6 and 12 percent. D-4