Dolores Archaeological Program Technical Reports, DAP-014: Climatic Reconstruction

Pollen records from two locations in the spruce (Picea engelmannii) forest of the La Plata Mountains, southwestern Colorado, provide paleoclimatic information for the headwater region of the Dolores River. Because of the difference in spruce growth response to climatic variation at its upper and lower elevational limits, the pollen records from Twin Lakes and Beef Pasture yield paleoclimatic information unobtainable from either record alone. Radiocarbon dates, tree-ring indices, and historic records give chronological control. Pollen ratios, tree-rings, and the climatic conditions described by Newberry and Macomb in 1859 for the Dolores Project area are used to reconstruct the history and magnitude of climatic change that has taken place from the Anasazi occupation to the present. The A.D. 800-1050 period was about as wet, but the A.D. 800- 1100 period was cooler than the present century. The A.D. 1050-1150 period was as wet and the A.D. 1100-1200 period was as warm as the 1920s. By A.D. 1250 the climate of southwestern Colorado was too cold and dry to successfully grow corn and remained so until the recent change in the climate to warmer and wetter conditions during the past 100 years or so.