Chapter Three Table of Contents

III. STUDY AREA DEFINITION

The study area occupies the north-central portion of the Great Basin physiographic province and straddles the states of Nevada, Utah, and Idaho (Figure 3.1). After accessing data quality and completeness of GIS and database files for the region, a final configuration, consisting of 12 hydrographic basins was decided upon (Table 3.1) Hydrographic unit boundaries are derived from United States Geological Survey data, compiled from 1:250,000 base maps in 1973. The study area encompasses an excellent cross-section of the Great Basin biome, though a small portion of the area lies outside of the Great Basin as a hydrographic entity (Figure 3.2). For the sake of simplicity, we have used the common abbreviation of “HUC” (hydrologic unit catalog) in much of the following reporting to mean an individual hydrologic unit catalog item, i.e., a hydrographic basin.

Our initial attempt at model development proposed that we employ broad, landscape level criteria to model the probability of encountering cultural resources over the broad reach of the entire study area. While grossly similar in terms of very general climate, vegetation, and topography, considerable variation is apparent as one moves from west to east and south to north across the study area. When contrasted by size, landform, and hydrologic regimes, the valleys in eastern Nevada bear little resemblance to either the Great Salt Lake basin, or the Upper Snake area. In order to maintain the landscape level approach but constrain environmental factors, the sub-basins within the study area were chosen as the analytical units rather than the larger study area as a whole.

Variations in topography define three hydrographic sub-regions within the study area; the Central Nevada Desert, Great Salt Lake and the Upper Snake. Each sub-region consists of a number of smaller hydrographic units, with boundaries based upon drainage patterns. Gross similarities in topography and drainage pattern and vegetation allowed for analysis of the Upper Snake and Great Salt Lake sub-regions as single units.

Internally drained basins and surrounding mountain ranges comprise the Central Nevada Desert sub-region. While grossly similar, each hydrographical basin within this sub-region contains significant variation in physiography that could effect human adaptation. Two hydrographic units in Nevada, Long/Ruby Valley and Spring/Steptoe Valley were treated separately so that we might better highlight variation between each area, and directly compare the results of this landscape modeling effort with more fine-grained modeling recently conducted in the Nevada basins of Pine Valley and Railroad Valley. The Pilot-Thousand Springs hydrographic unit within the Great Salt Lake sub-region showed a closer affinity to Central Nevada units and was likewise analyzed as a distinct entity.

III. STUDY AREA DEFINITION

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