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~l t..j Chapter 1 Major Physical, Legal, and Institutional Characteristics _~.,t' r~ .~"i The Upper Rio Grande Basin stretches for about 1,000 miles, from the headwaters in southern Colorado, through central New Mexico, to Ft. Quitman, 100 miles below El Paso, Texas, on the U.S.-Mexico border. The Basin's climate is semi-arid or arid and its water and related resources have been essential elements of the local and regional economies for hundreds of years. In the next chapter we discuss the nature of the competition for these resources and, in Chapter 3 we discuss the major problems associated with this competition. In this chapter we set the stage for those discussions by describing the Basin's major physical characteristics, providing a short history of human development in the Basin, and describing the major laws and institutions that govern resource use. A. Major Physical Characteristics !.~. In this section we briefly describe the overall character of the Basin's ecosystem, surface-water flows, and groundwater supplies and uses. 1. Ecosystem ::i ,j The diversity and complexity in elevations, geology, topography, and precipitation levels across the Basin result in an intricate vegetation pattern. The reach ofthe river from the headwaters in southern Colorado to the southern end of New Mexico's Middle Rio Grande Valley contains sections of montane grassland, coniferous woodland, and mixed conifer. Spruce-fir (subalpine) forest adjoins these sections at higher elevations. Downstream, the Basin becomes more desert-like, with basin and plains vegetation adjacent to the river's riparian zone. ~ - A comprehensive assessment of ecological conditions in the Basin has not been completed, although some areas have been studied extensively. The sketchy evidence shows that much of the ecosystem has been severely modified, especially since the middle ofthe last century. Some reaches are commonly labeled as "dead" or "bombed out." These occur in all parts of the Basin. There are highland tributaries, such as the Alamosa River in southern Colorado, that exhibit reduced water quality and loss of natural habitat because of extensive channelization, loss of riparian vegetation, and acid mine drainage. In much of New Mexico, channelization and the operation of dams have altered the river's fundamental bio-physical {1:2881