U.S. Department of the Interior Bureau of Land Management Paleontological Resources Technical Report Riley Ridge to Natrona Project DECEMBER 2018 Table of Contents 1.0 Introduction ......................................................................................................................................... 1 2.0 Regional Setting .................................................................................................................................. 1 3.0 Inventory Methodology ....................................................................................................................... 1 4.0 Potential Fossil-Bearing Geologic Formations ................................................................................... 4 4.1 Browns Park Formation (PFYC 3) ............................................................................................ 4 4.2 White River Formation or Group (PFYC 5) .............................................................................. 5 4.3 Wind River Formation (PFYC 5) .............................................................................................. 5 4.4 Green River Formation (PFYC 5) ............................................................................................. 5 4.5 Wasatch Formation (PFYC 5) ................................................................................................... 5 4.6 Battle Spring Formation (PFYC 3)............................................................................................ 6 4.7 Bridger Formation (PFYC 5) .................................................................................................... 6 4.8 Crooks Gap Conglomerate (PFYC 3) ........................................................................................ 6 4.9 Fort Union Formation (PFYC 3) ............................................................................................... 6 4.10 Mesaverde Formation or Group (PFYC 3) ................................................................................ 6 4.11 Lance Formation (PFYC 5) ....................................................................................................... 6 4.12 Lewis Shale (PFYC 5) ............................................................................................................... 7 4.13 Cody Shale (PFYC 3) ................................................................................................................ 7 4.14 Mowry and Thermopolis Shales (PFYC 3) ............................................................................... 7 4.15 Cloverly, Morrison, and Sundance Formations (PFYC 5) ........................................................ 7 4.16 Frontier Formation (PFYC 3) .................................................................................................... 7 4.17 Chugwater and Dinwoody Formations (PFYC 3) ..................................................................... 7 4.18 Segment 1: Riley Ridge Treatment Plant to the Proposed Riley Ridge Sweetening Plant ....... 8 4.19 Segment 2: Proposed Riley Ridge Sweetening Plant to the Bairoil Interconnect ..................... 9 4.20 Segment 3: Bairoil Interconnect to the Lost Cabin/Natrona Hub Interconnect ......................... 9 5.0 Literature Cited ................................................................................................................................. 11 Tables Table 4-1 Geological Units and Associated Potential Fossil Yield Classification in the Study Area ........................................................................................................................................ 8 Riley Ridge to Natrona Project i November 2018 Paleontological Resources Technical Report THIS PAGE INTENTIONALLY LEFT BLANK List of Acronyms and Abbreviations Applicant Riley Ridge LLC and PacifiCorp, doing business as Rocky Mountain Power BLM Bureau of Land Management CO2 carbon dioxide Denbury Riley Ridge LLC PFYC potential fossil yield classification Project Riley Ridge to Natrona Project (also RRNP) RRNP Riley Ridge to Natrona Project Riley Ridge to Natrona Project iii November 2018 Paleontological Resources Technical Report THIS PAGE INTENTIONALLY LEFT BLANK 1.0 Introduction The Bureau of Land Management (BLM) prepared this technical report for paleontological resources to support the preparation of an Environmental Impact Statement in response to three applications for right- of-way submitted by Riley Ridge LLC (Denbury) and PacifiCorp, doing business as Rocky Mountain Power (collectively referred to as the Applicant), for the Riley Ridge to Natrona Project (RRNP or Project). The Applicant’s proposal to construct and operate the Project, including the underground carbon dioxide (CO2) pipeline system and Riley Ridge Sweetening Plant, the 230-kilovolt transmission line, injection wells, and ancillary facilities. The paleontological resources found within the 2-mile-wide study corridors of the Project and alternative routes representing the affected environment are described in this technical report. 2.0 Regional Setting The Project would cross the Greater Green River Basin, the Beaver Divide, and the Wind River Basin. Both basins have a wide variety of Mesozoic and Cenozoic geological units that have been known to produce fossils in the past. The Greater Green River Basin was filled with Paleocene and Eocene fluvial and lacustrine sediments (Murphey and Daitch 2007). The Wind River Basin consists mostly of Eocene basin-fill sediments in the flat-lying, lower areas with belts of folded Precambrian, Paleozoic, and Mesozoic rocks forming the flanks and cores of the adjacent mountain ranges (Keefer 1970). The escarpment called the Beaver Divide (Beaver Rim) is at the southern margin of the Wind River Basin and mostly includes a series of Tertiary sediments (Emry 1975). 3.0 Inventory Methodology Information for the paleontological inventory was obtained from a review of the scientific literature and geologic maps, a record search from the Department of Geology and Geophysics at the University of Wyoming, a Paleontological Resource Assessment previously done for the Project (Erathem-Vanir Geological Consultants 2012), and a geology resource report (SCWA 2014). Agencies contacted include the U.S. Geological Survey, BLM, and Wyoming State Geological Survey. Information about the geological units and known fossil localities were used to identify the paleontological potential in areas that would be affected by the Project. Paleontological potential levels were assigned to each geological unit using the potential fossil yield classification (PFYC) adopted by the BLM for assessing paleontological potential on federal lands (WO IM 2016-124). The PFYC is a five- tiered system (1 to 5) classifying geological units based on relative abundance of vertebrate fossils or scientifically significant invertebrate fossils and plant fossils, and their potential to be adversely affected, with a higher class number indicating a higher potential. This classification is applied to a geological formation, member, or other distinguishable map unit, preferably at the most detailed level that can be mapped. It is not intended to be applied to specific paleontological localities or small areas within the units. Although significant localities may occasionally occur in a geologic unit, a few widely scattered important fossils or localities do not necessarily indicate a higher class; instead the relative abundance of significant localities is intended to be the major determinant for the class assignment. Because of the direct relationship that exists between paleontological resources and the geological units they are found within, and by knowing the geology of an area and the fossils previously found in a geological unit, it is possible to predict where fossils likely would be found. The PFYC system is meant to provide baseline guidance for predicting, assessing, and mitigating paleontological resources. The classification should be Riley Ridge to Natrona Project 1 November 2018 Paleontological Resources Technical Report considered at an intermediate point in the analysis and should be used to assist in determining the need for further mitigation assessment actions (WO IM 2016-124). Each class is defined as follows: Class 1 – Very Low. Geologic units that are not likely to contain recognizable fossil remains. ▪ Units that are igneous or metamorphic, excluding reworked volcanic ash units. ▪ Units that are Precambrian in age or older. (1) Management concern for paleontological resources in Class 1 units is usually negligible or not applicable. (2) Assessment or mitigation is usually unnecessary except in very rare or isolated circumstances. The probability for impacting any fossils is negligible. Assessment or mitigation of paleontological resources is usually unnecessary. The occurrence of significant fossils is non-existent or extremely rare. Class 2 – Low. Sedimentary geologic units that are not likely to contain vertebrate fossils or scientifically significant nonvertebrate fossils. ▪ Vertebrate or significant invertebrate or plant fossils not present or very rare. ▪ Units that are generally younger than 10,000 years before present. ▪ Recent aeolian deposits. ▪ Sediments that exhibit significant physical and chemical changes (i.e., diagenetic alteration). (1) Management concern for paleontological resources is generally low. (2) Assessment or mitigation is usually unnecessary except in rare or isolated circumstances. The probability