THE ANCIENT I'EOlM.KS. 21 



Distribution. 



As might be expected in a semi-arid region the agri- 

 cultural population in prehistoric times was concen- 

 trated at the higher elevations where the rainfall was 

 the greatest and in the river valleys where irrigation 

 could be easily practised. 



San Juan. One of the most important regions 

 anciently occupied was that watered b}' the northern 

 tributaries of the San Juan River. These streams are 

 fed by the snows of the mountains of southern Colorado 

 and Utah. At some distance from their sources they 

 are confined in sheer-walled canj^ons which unite with 

 each other as they approach the San Juan which enters 

 the Colorado above the Grand Canyon. Some of the 

 ruins are on the tablelands between the streams, others 

 are at the head of the canyons, and man}^ are in the 

 canyons themselves either on their floors or under their 

 overhanging walls. The Cliff Palace and the Spruce 

 Tree House, two of the largest and best known cliff- 

 ruins, are in this region. 



In Chaco Canyon, a branch of Chaco ^^alle3^, there 

 is a cluster of eleven large ruins which evidently repre- 

 sent an important political group of prehistoric villages. 

 One of these, Pueblo Bonito, is hardly surpassed in size 

 and interest anywhere. Canyon de Chelly which joins 

 Chinlee Valley has many ruins both on the floor of the 

 valley and under the walls. 



Rio Grande. On the western side of the Rio Grande 



