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Figure 4.3. Diversion weir for floodplain irrigation.  tion, numerous pre-Hispanic people not only made maps on a variety of materials (Glass 1975: 33-36), but also main- tained cartographic records of agricultural lands that were more detailed than European records of the time (Coe 1964: 93, 96; Harvey and Williams 1980).  Although the exact agricultural procedures used prehistor- ically in the Valley of Sonora are not known, analogs drawn from present-day inhabitants who use traditional techniques and ethnohistoric comparisons with people from neighbor- ing areas offer probable parallels. Stone axes that were found during the survey and were uncovered during excavations probably were used to clear the riparian woodlands (Pen- nington 1980: 143). As mentioned in Chapter 3, fields were irrigated by canals leading from diversion weirs constructed across the river channel (Fig. 4.3). Weirs probably were built by driving short stakes into the riverbed to form a diagonal barrier across the flow of the river (Bahre 1984: 62). Branches were woven among the stakes, and low earth was mounded atop and downstream of the brush. Because gaps were left in these structures to allow excess water to escape,

Figure 4 3. Diversion weir for floodplain irrigation. tion, numerous pre-Hispanic people not only made maps on a variety of materials (Glass 1975: 33-36), but also main- tained cartographic records of agricultural lands that were more detailed than European records of the time (Coe 1964: 93, 96; Harvey and Williams 1980). Although the exact agricultural procedures used prehistor- ically in the Valley of Sonora are not known, analogs drawn from present-day inhabitants who use traditional techniques and ethnohistoric comparisons with people from neighbor- ing areas offer probable parallels. Stone axes that were found during the survey and were uncovered during excavations probably were used to clear the riparian woodlands (Pen- nington 1980: 143). As mentioned in Chapter 3, fields were irrigated by canals leading from diversion weirs constructed across the river channel (Fig. 4.3). Weirs probably were built by driving short stakes into the riverbed to form a diagonal barrier across the flow of the river (Bahre 1984: 62). Branches were woven among the stakes, and low earth was mounded atop and downstream of the brush. Because gaps were left in these structures to allow excess water to escape,