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Reclamation for Sugar Loaf (Turquoise Lake) and Twin Lakes dams. These studies included regional synthesis of tectonic and seismicity data, short-term microseismic monitoring, regional lineament and fault studies and trenching of potentially seismogenic faults in the upper Arkansas Valley near Buena Vista. The report of these studies, however, has not been finalized and released in its entirety. Several memoranda related to assessment of seismic hazards for individual projects (Sugaz Loaf Dam near Leadville and Twin Lakes Dam near Granite), however, have been prepared by USBR (1980, 1990). In the Spring of 1980, the U.S. Department of Energy awarded a contract to Dames and Moore for evaluation of earthquake hazards in the vicinity of the Rocky Flats Plant. This study (Dames & Moore, 1981) demonstrated the main trace of the Golden fault is inactive, but left the origin of other tectonic features unanswered. Moreover, the report itself generated some controversy over the size and location of a major historic (1882) earthquake felt in Denver, the Southern Rockies and central Great Plains. Studies conducted by McCalpin (1981, 1982) in the San Luis Valley indicate major earthquakes (Richter magnitude M~ 6.6 to 7.0) have occurred at intervals ranging from 2500 to 60,000 years with the most recent even[ occurring 7600+120 ybp. The U.S. Geological Survey (Colman, 1985; Colman and others, 1985) published maps showing tectonic features of late Cenozoic (<27+ mybp) origin in Colorado and details of seismogenic faulting in the Rio Grande rift. The regional work is mainly a recapitulation of earlier studies, notably Kirkham and Rogers (1981), but does incorporate up-to-date interpretations and portrays both the late Eocene erosion surface and Miocene and younger rocks deposited in structural basins. The Colorado Geological Survey published a series of earthquake- related studies in the mid-1980s, including data on Colorado earth- quakes (Bulletin 46; Kirkham and Rogers, 1985), an interpretation of the November 7, 1982, earthquake (Open-File Report 86-8; Kirkham and Rogers, 1986), and a seazch for historical felt reports for selected earthquakes (Information Series 23; Oaks and Kirkham, 1986). These reports along with earthquake data bases maintained by the National Earthquake Information Center (USGS) provide the basis for evalua- tion of past and future earthquake occurrence in Colorado. 7