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y .a L r Figure 16. Honey mesquite habitat being cleared for agriculture. Piles are burned and new saltcedar and arrowweed growth are rebulldozed. The land is then leveled and planted. Photo by D. Krueper. and vast tracts between the towns of Parker and Ehrenberg continued to be cleared, although recent declines in farm crop prices have slowed the process. Total agriculture production on the lower Colorado River was about 120,000 ha (300,000 acres) by 1986. Most of the production is in alfalfa, cotton, and winter wheat, three crops that require vast amounts of Irriga- tion water. In order to more fully manage the Colorado River, engineers began to fine-tune control of the river in the 1950's through riprapping (i.e., to armor banks with large rocks) to stabilize banks, thereby minimizing channel shifts and reducing sediment transport. In areas where the channel was highly braided or contained num- erous oxbows, it was deepened by dredging or a new channel was cut. In many places, old oxbow lakes or mar- shes lateral to these channels rapidly drained because the water table was lowered as new channels were cut or existing ones deepened. Finally, many canals were lined with concrete to re- duce seepage losses (Figure 17). In addition to agricultural devel- opment, the lure of mild year-round temperatures and an abundance of water for recreation has caused an increase in urbanization in many parts of the valley. Numerous trailer parks and various resorts now accommodate an annual migration of winter vacationers from northern states, as well as a growing number of year-round residents (Figure 18). Development of these communities has resulted in the clear- ing of additional riparian vegetation 18