26 INDIANS OF THE SOUTHWEST. 
enough to make the surface of the walls even. Where 
the walls were thick the two surfaces were often well 
built and the intervening space filled roughly with any 
available material. Some of the walls show regular 
courses of large stones alternating with courses of smaller 
Square Watch Tower. San Juan River. 
(Courtesy of Dr. Prudden.) 
ones producing a banded effect, evidently intentionally 
decorative. 
Along the lower Gila and Salt Rivers bedrock as a 
source of building material was not available and 
round river boulders were used, the greater part of the 
