FuwEns] CASA GRANDE MOUNDS alts 
parts of these were well-preserved. The existence of a narrower 
channel in the bed of a large ditch, through which the water could run 
when the supply was small, was seen elsewhere by the present writer. 
The main ditches were large enough for irrigation when full of water 
and doubtless were used for that purpose. Not far from Blackwater 
is a hill, surrounded by a prehistoric ditch above the level of the plain, 
around which the ditch was dug to avoid a too rapid descent. 
The testimony of the old men consulted supports the theory that 
the ancient irrigation ditches were dug by means of wooden shovels 
similar to those mentioned and figured later in this report, the earth 
probably being carried to a distance by the women and children. 
The present Pima say that they now organize to construct irrigation 
ditches in a way somewhat similar to that of the ancients. As all 
clans enjoy the advantage of the water thus obtained, every clan has 
its representatives in constructing the canals, and failure to work 
involves loss of water right, although a clan may be represented by 
members of other clans. The amount of labor necessary in the con- 
struction of new ditches is settled in council, in which all clans inter- 
ested take part. 
The construction by the ancients of the great irrigation ditches led 
to greater cooperation of labor in the Gila-Salt Valley than anywhere 
else in the prehistoric Southwest. This union of many men under 
a chief, with equal representation in council, led to an advanced social 
organization and culture, a degree of culture which would not have 
been realized so soon under less favorable conditions. This coop- 
eration and resultant organization made possible also the building of 
the great compounds and the massive structures they inclosed. 
Excavation of one of the banks of an irrigation ditch near Casa 
Grande shows successive layers of soil and small stones, indicating 
repeated clearing out of the canal. The layers of stone may have 
been necessary to prevent the earth washing into the channels. 
These were also continually filing up with mud and detritus from 
the river, the amount of which was considerable when the Gila was 
swollen. The head-gates were probably made of posts and brush, 
not unlike the gates constructed at the present day by the Pima and 
the Maricopa. 
Closely connected with the irrigation ditches are the reservoirs 
(vashki), of which there are one or more near every large group of 
compounds in the Gila-Salt Basin. These reservoirs are shallow 
depressions in which rain water collects, but were not always con- 
nected with the irrigation ditches. Drinking water was probably 
obtained from these and other receptacles. 
