Chapter 3—Affected Environment
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Proposed RMP/Final EIS Chapter 3 CHAPTER 3—AFFECTED ENVIRONMENT 3.1 INTRODUCTION This chapter describes the existing resource conditions, resource uses, special designations, and socioeconomic conditions of lands administered by Price Field Office (PFO). The affected environment serves as the baseline of existing conditions for analyzing the impacts of the alternatives. 3.1.1 Overview of the Planning Area The PFO encompasses approximately 2.5 million acres within Carbon and Emery counties, which are located in central-eastern Utah. The Green River on the east, the Manti-La Sal National Forest on the west, and the Carbon–Duchesne county line on the north bound the PFO. The Emery–Wayne county line borders the south (Map 1-2). Interstate 70 (I-70) traverses the southern half of the PFO. State highway SR-10 and federal highway US-6 are located within the PFO. A number of noted features are located within the area, including the Book Cliffs, West Tavaputs Plateau, San Rafael Swell, Range Creek, Nine Mile Canyon, Desolation Canyon, Labyrinth Canyon, Price River Canyon, and Cleveland-Lloyd Dinosaur Quarry. Based on the modified Köppen Classification System (1987a), the Wasatch Plateau and Book Cliffs of the PFO are characterized as undifferentiated highlands. The central and northern portions of the PFO have steppe climates, and the southeast portion of the PFO has a desert climate. Elevations in the PFO range from approximately 4,060 feet at the City of Green River to more than 10,400 feet at East Mountain. The majority of the PFO is drained by the Green River, including discharges from the Price River and San Rafael River. The Green River eventually drains into the Colorado River south of the PFO in Canyonlands National Park. Muddy Creek discharges south into the Dirty Devil River, which joins the Colorado River about 2 miles north of Hite, Utah, in Glen Canyon National Recreation Area. Physiography and Geology The PFO lies within the Colorado Plateau physiographic province (Map 3-1). More recently, Stokes (1986) refined the physiographic sections within the State of Utah for the Colorado Plateau, Rocky Mountain, and Basin and Range Provinces. Carbon and Emery counties include four sections within the Colorado Plateau (i.e., Book Cliffs/Roan Plateau, Mancos Shale Lowlands, San Rafael Swell, and Green River Desert), and one physiographic section that is considered transitional between the Colorado Plateau and Basin and Range (i.e., the Wasatch Plateau section). In addition, a very small section of the Circle Cliffs-Teasdale Anticline Section of the Colorado Plateau cuts the extreme southwest corner of the PFO. A dominant physical feature within the PFO is the San Rafael Swell, occupying the majority of Emery County. This feature is a large northeast trending upward approximately 75 miles long and 30 miles wide that is part of a much larger, double-plunging anticline structure. This large, regional fold exposes rocks of the Pennsylvanian age through the Cretaceous age (Maps 3-1, 3-2, and 3-3). Resistant beds of sandstone are exposed as hogbacks on the steeply upturned east flank of the anticline and are referred to locally as “reefs.” Three perennial rivers (i.e., Muddy, San Rafael, and Price) flow eastward into the Green and Colorado River system (Map 1-1). Price RMP 3-1 Chapter 3 Proposed RMP/Final EIS Bordering the San Rafael Swell on the north, west, and northeast sides is the Mancos Shale Lowland section, including Castle Valley and Clark Valley. The Upper Cretaceous Mancos Shale is an easily eroded rock formation and is exposed at the surface across much of this section, resulting in relatively low-lying areas. The landscape of the Mancos Lowlands is characterized by sloping, gravel-covered pediments, rugged badlands, and flat-bottom alluvial valleys (Stokes 1988). Immediately southeast of the San Rafael Swell lies the Green River Desert Section of the Colorado Plateau, characterized by Quaternary eolian deposits (Maps 3-2 and 3-3) with scattered mesas and buttes of Jurassic bedrock exposed at the surface. To the north of the Mancos Shale Lowlands lies the Book Cliffs and Roan Plateau section of the Colorado Plateau. This area constitutes the southern extension of the Uinta Basin where Upper Cretaceous and Lower Tertiary rocks (Maps 3-2 and 3-3) rise upward from the north along the dip slopes of the basin to reach elevations of 8,000 to 10,000 feet. On their south end, these rocks are abruptly truncated in great erosional cliffs that descend to elevations around 5,000 feet in the Mancos Lowlands. The Book Cliffs are formed by Upper Cretaceous sandstones and shaly siltstones of the Mesaverde Group, including the Blackhawk Formation, Castlegate Sandstone, and the Price River Formation. To the northeast of the Book Cliffs, the Roan Cliffs are formed by the reddish-brown mudstone and sandstone beds of the Colton Formation (Paleocene-Eocene) (Maps 3-2 and 3-3). Further to the northeast in Carbon County are other erosional rises, including the West Tavaputs Plateau and the Bad Land Cliffs that expose the Eocene Green River Formation. Along the west margin of the PFO is the Wasatch Plateau section transitioning between the Colorado Plateau and Basin and Range physiographic provinces (Stokes 1986). The area displays some features typical of the Great Basin, such as extensional tectonics and north-south trending normal faults. The steep eastern margin of the Wasatch Plateau is a continuation of the Book Cliffs escarpment and is an erosional feature not related to faulting (Stokes 1986). The Circle Cliffs-Teasdale Anticline physiographic section lies in the extreme southwest corner of Emery County (Map 3-2). This anticlinal structure is similar to the San Rafael Swell but shorter and narrower, and its axis trends northwest (Stokes 1986). Climate The PFO is located in central Utah, east of the Wasatch Mountains. The proximity of the Wasatch Mountains exerts a strong influence on the climate and weather of the area. Areas east of the Wasatch Range are characterized by hot, dry summers and cold, dry winters. Air movement at this latitude is predominately from the west and northwest year-round. The lower elevations receive less than 10 inches of precipitation annually. Higher elevations of the PFO receive more than 14 inches of precipitation annually. Snow amounts also are low east of the Wasatch Mountains. Average maximum temperatures in the area range from 97°F in July to 33°F in January. Average minimum temperatures range from 7°F in January to 58°F in July (BLM 1997, BLM 1999b). Detailed climate and meteorological data can be found in the Final Air Quality Baseline and Analysis Report – Price Resource Management Plan (Booz Allen 2008). Global Climate Change On-going scientific research has identified the potential impacts of climate changing pollutants on global climate. These pollutants are commonly called “greenhouse gases” and include carbon dioxide (CO2); methane; nitrous oxide; water vapor; and several trace gas emissions. Through complex interactions on a 3-2 Price RMP Proposed RMP/Final EIS Chapter 3 regional and global scale, these emissions cause a net warming effect of the atmosphere, primarily by decreasing the amount of heat energy radiated by the Earth back into space. Although climate changing pollutant levels have varied for millennia (along with corresponding variations in climatic conditions), recent industrialization and burning of fossil carbon sources have caused CO2 concentrations to increase dramatically, and are likely to contribute to overall climatic changes, typically referred to as global warming. Increasing CO2 concentrations also lead to preferential fertilization and growth of specific plant species. Global mean surface temperatures have increased nearly 1.0°C (1.8°F) from 1890 to 2006 (Goddard Institute for Space Studies, 2007). However, observations and predictive models indicate that average temperature changes are likely to be greater in the Northern Hemisphere. Figure 3-1 demonstrates that northern latitudes (above 24° N ) have exhibited temperature increases of nearly 1.2°C (2.1°F) since 1900, with nearly a 1.0°C (1.8°F) increase since 1970. Without additional meteorological monitoring systems, it is difficult to determine the spatial and temporal variability and change of climatic conditions, but increasing concentrations of these “greenhouse gases” are likely to accelerate the rate of climate change. The Intergovernmental Panel on Climate Change (IPCC) has recently completed a comprehensive report assessing the current state of knowledge on climate change, its potential impacts, and options for adaptation and mitigation. At printing of this Proposed RMP/Final EIS, this assessment is available on the IPCC web site at http://www.ipcc.ch/. According to this report, global climate change may ultimately contribute to a rise in sea level, destruction of estuaries and coastal wetlands, and changes in regional temperature and rainfall patterns, with major implications to agricultural and coastal communities. The IPCC has suggested that the average global surface temperature could rise 1 to 4.5 degrees Fahrenheit (°F) in the next 50 years, with significant regional variation. The National Academy of Sciences (2006) has confirmed these findings, but also indicated that there are uncertainties regarding how climate change may affect different regions. Computer models indicate that such increases in temperature will not be equally distributed globally, but are likely to be accentuated at higher latitudes, such as in the Arctic, where the temperature increase may be more than double the global average (BLM 2007c). Also, warming during the winter months is expected to be greater than during the summer, and increases in daily minimum temperatures is more likely than increases in daily maximum temperatures. Vulnerabilities to climate change depend considerably on specific geographic and social contexts. BLM recognizes the importance of climate change and the potential effects it may have on the natural environment.