A paleomagnetic investigation of in-situ and exploration drill core samples of the Wilkins Peak Member of the Ecocene Green River Formation in the Green River Basin of Wyoming yielded poor and unreliable paleomagnetic results. X-ray and thermomagnetic analysis of samples from the study shows that pyrrhotite is the dominant magnetic mineral in the samples; pyrrhotite is known to be a common authigenic phase in Green River Basin sediments. Two earlier studies of the Green River Formation suggest unexpected behavior of the Eocene magnetic field; magnetite was identified in one sample of the former study. Similar lithologies have been sampled by all three studies. Because magnetic mineralogy may vary from authigenic to primary within one rock type, it is important for future paleomagnetic studies of the Green River Formation to carefully investigate the mineralogy and timing of remanence acquisition.