All available data on the Colorado earthquake of November 7, 1882 indicate an epicentral location in northwestern Colorado and a local magnitude (ML) of about 6½. There are few descriptive reports from the meisoseismal region because the area was sparsely populated at the time. An epicenter of 40.5°N, I 08°W has been estimated based on the distribution of Modified Mercalli intensities in Colorado, Wyoming, and Utah. This epicenter is uncertain by at least I 00 kilometers (km). The estimated felt area of 500,000 square km suggests ML is approximately 6½ based on a comparison with more recent, better documented earthquakes in the Rocky Mountain region. This magnitude estimate is uncertain by at least one-half magnitude unit clue to uncertainty in the felt area estimate and in the felt area-magnitude relationship. Given the dearth of earthquake reports in the epicentral region, the exact location will remain uncertain until a causative fault, with documented movement about I 00 years ago, is identified. One possible causative structure is located in the Piceance Basin in northwest Colorado. The fault was identified by investigation of satellite images and field reconnaissance after the preliminary epicenter had been identified. The 1882 shock is the largest earthquake documented in Colorado; a recurrence today would affect many engineering facilities in the Rocky Mountain region.