The largely subterranean nature of the mycorrhizal fungal life form impedes efforts to monitor protected fungi and evaluate the effectiveness of mitigations in timber harvest areas. In this study we developed and tested a multiplex PCR system capable of detecting 14 listed Phaeocollybia species in soil. We then investigated the persistence of Phaeocollybia species at three sites in northwestern Oregon where Phaeocollybia attenuata and other Phaeocollybia sporocarps had been observed prior to timber harvest. The three sites had three different levels of protection for the fungi. One site was in a buffer zone next to a thinned area, one was within a thinned area, and one was in a clearcut area. The method was effective at detecting the target species in soil. We detected Phaeocollybia species in the soil at all sites, even in the clearcut after 12 yr, during which no sporocarps were observed.