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and of low to moderate level. No earthquake exceeding MM intensity VII has occurred in Colorado in the past 100+ yeazs (Hadsell, 1968). The seismic history of the Rio Grande rift in Colorado is short and sparse. The only macroearthquakes associated with the Colorado portion of the rift are the MM intensity VI-VII event of 1901 near Buena Vista, the MM intensity IV event of 1961 northeast of Buena Vista, and the MM intensity V (mb=4.3) event of 1985 neaz Salida. Kirkham and Rogers (in preparation) describe these historic earth- quakes in and near the Upper Arkansas Valley graben: November 15, 1901 Numerous newspapers published accounts of an earthquake felt in and near Buena Vista on November I5. 1901 (Oaks and Kirkham, 1986). It is somewhat difTicult to discriminate the felt reports of the November 13 and 14 events from those for the November l5 earthquake. It is our interpretation that the felt reports from Buena Vista and Cottonwood Lake are for a distinct earthquake on November IS that was felt only in that immediate area. It is possible, but we believe unlikely, that the date of the Buena Vista report is incorrect and that these felt reports resulted from the Utah earthquakes on November 13 and 14. An interesting aspect of this earthquake is that moderate intensities (VI) are reported for this event in the immediate vicinity of Buena Vista, but that surrounding towns did not report the event. Many residents of Buena Vista ran excitedly into the streets wearing only night clothes. and a large plate glass window was broken. The water in Cottonwood Lake was agitated, and numer- ous boulders rolled down Mount Princeton and Mount Harvard. Newspapers in Salida described the effects in Buena Vista, but did not report any local effects (Salida Mail. November 19. 1901). Likewise, newspapers in both Leadville and Aspen failed to mention any local manifestations to the earthquake. Such evidence suggests the Buena Vista earthquake may have occurred at a fairly shallow depth and may have been only magnitude 4.0 to 5.0 or perhaps even smaller. November 27, 1961 Central Colorado was shaken by an earthquake on November 27. 1961.. . Intensity IV shaking was reported at Buena Vista, Leadville, Fairplay, Jefferson, Hansel, Alma, Garo, and at other rural locations (Lander and Cloud, 1963). Aftershocks were felt in Jefferson and Hansel. The epicenter was reportedly located about 10 km northeast of Buena Vista, near the east side of the Upper Arkansas Valley. The earthquake was felt over at least 4,800 km=. March 16. 1985 On March 13, 1985 a small earthquake shook the Salida area. The quake was felt over 2.200 km= with intensity V reported at Salida and Texas Creek. The l8