Water-resources data-collection activities for October 1, 1979, through September 30, 1980, are summarized for Colorado and bordering States. Fifty-four interpretive hydrologic investigations include: 9 statewide investigations, 6 regional investigations, 11 investigations in the Missouri River basin, 7 investigations in the Arkansas River basin, 3 investigations in the Rio Grande basin, 16 investigations in the Colorado River basin, and 2 multistate investigations. The summaries of the investigations consist of a map showing the location of the areas of investigations and a brief description of the investigation's purpose, objective, approach, progress, and plans.