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Vantage to Pomona Heights Chapter 3 230 kV Transmission Line Project FEIS Affected Environment PAGE 3-291 3.15 GEOLOGY AND SOILS As was done in the Draft Environmental Impact Statement (DEIS) and Supplemental Draft Environmental Impact Statement (SDEIS), this section describes the existing conditions (affected environment) and considers issues related to geology and soils along all Action Alternatives presented in the DEIS and SDEIS, including those raised during scoping. This Final Environmental Impact Statement (FEIS) section consolidates and builds on the information presented in the January 2013 DEIS as well as the January 2015 SDEIS and includes references to those documents throughout the text where appropriate. This FEIS identifies the New Northern Route (NNR) Alternative – Overhead Design Option as the Environmentally Preferred Alternative and the U.S. Bureau of Land Management (BLM) has selected the NNR Alternative – Overhead Design Option as the Agency Preferred Alternative. 3.15.1 Data Sources The evaluation was conducted using digital data sources and previously conducted studies. Sources reviewed included the Soil Survey of Yakima Training Center, parts of Kittitas and Yakima Counties, Washington (Natural Resources Conservation Service [NRCS] 2006); the NRCS Web Soil Survey; soil data from the NRCS for Yakima County, Grant County, Benton County, Kittitas County and the Yakima Training Center (NRCS 2009); an article on the geology of the Terrace Heights community near the City of Yakima (Lind and Vachon n.d.); and geologic maps of the Priest Rapids (Reidel and Fecht 1994) and Yakima (Walsh 1986) quadrangles from the Washington State Department of Natural Resources (DNR). The Washington Division of Geology and Earth Resources (WDGER), a division of the DNR, maintains information about the existing geology and geologic hazards in the state of Washington. Data from WDGER that was used included surface geology at scale 1:100,000, landslides at scale 1:24,000, seismogenic features consisting of active faults, and ground response including liquefaction susceptibility. For the purposes of this document, a six-mile wide buffer (three miles each side of route segment centerlines for the Action Alternatives) is the Project study area and was analyzed for potential impacts to geology and soils. 3.15.2 Current Conditions and Trends, Regional Overview 3.15.2.1 Geology The Project study area is located in the Columbia Plateau physiographic province. The geology of the Project study area consists of interbedded volcanic and sedimentary rocks of the Columba River Basalt Group. The Columbia River Basalt formed when lava erupted intermittently out of north-northwest- trending fissure systems across southeastern Washington and adjacent portions Idaho and Oregon during the Miocene Epoch (17 to 6 million years ago). About the time of the last basalt flow, the Cascade Range became active again and mudflows and pyroclastic material were interfingered with basalt flows. Streams carried this lighter material towards the eastern lowlands, creating the uppermost portion of the Ellensburg Formation (NRCS 2006). Tectonic forces caused enough steady north-south compression to fold the basalt like an accordion from Toppenish to Ellensburg, forming ridges (anticlines) and valleys (synclines). The Yakima Ridge is part of the long, parallel ridges of the Yakima Fold Belt. The Yakima Fold Belt includes anticlinal ridges within the Project area. Generally from south to north they include the Yakima, Umtanum, Saddle Mountain, and Manastash Ridges. Yakima Ridge is the southern ridge of the ridges in the Project study area. As the Yakima ridge rose and the Yakima River eroded down through the resistant basalt, the Yakima River deposited a flat layer of cobbles, gravels, pebbles and silts onto its floodplain, which eventually rose in elevation due to uplift, out of reach of the river, resulting in a terrace (Lind and Vachon n.d.).