Chapter 1. Introduction
5
1.4
PROJECT AREA
The area broadly covered by this review includes all or portions of ten semi-
arid western states: Arizona, California, Colorado, Idaho, Nevada, New Mexico,
Oregon, Texas, Utah, and Wyoming (Fig. 1). This region encompasses multiple
physiographic provinces and is characterized by spatially and seasonally variable
moisture sources that produce a highly variable rainfall pattern markedly differ-
ent from that in the eastern U.S. (Chapter 2). The region generally falls within the
Dry Domain and four Divisions--Tropical/Subtropical Steppes, Tropical/
Subtropical Deserts, Temperate Steppes, Temperate Deserts, and their associated
mountains--of the Ecoregions of the United States (Bailey 1995) and within the
Western Range and Irrigated Region and California Subtropical Fruit, Truck, and
Specialty Crop Region of the USDA Land Resource Regions (Soil Conservation
Service 1981).
Figure 1. Area covered by this review.
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