The United States has become acutely aware of its dependence on critical minerals and the associated risks of relying on global markets. A mineral is deemed critical if it faces vulnerabilities in the supply chain, plays a vital role in manufacturing, is irreplaceable, or its absence poses a threat to national security. To mitigate these risks, the U.S. government has launched initiatives to identify domestic sources and streamline permitting processes for traditional mining operations. Exploring potential sources, such as pre-existing quarries and mines, for rare earth elements (REEs) presents an opportunity to reduce costs and environmental impact compared to establishing new mining sites. This study investigates the potential presence of REEs in the Cretaceous-age coal seams of the Elk Basin Oil field in Park County, Wyoming. Of particular interest are exposures in the Late Cretaceous Eagle Formation. The Eagle Formation is a light gray to tan coarse-grained sandstone with iron concretions and sporadic coal seams deposited in terrestrial and deltaic environments. Elk Basin is a century-old active oilfield with well-exposed lignite seams. Portable X-ray fluorescence (pXRF) instrumentation permits rapid analysis of the elemental composition of rocks and identification of REEs. XRF is a widely used non-destructive device for analyzing the composition of solid and fluid materials. The application of XRF in this study focuses on recognizing associations between lignite coal seams and the occurrence and concentration of REEs. It is anticipated that REE occurrences will vary by both coal type and depositional environments in a predictable manner.