A Ghost of Caribou by Alice Henderson

Wildlife biologist Alex Carter is hired to see if there are any mountain caribou living in the Selkirk Wildlife Sanctuary in Washington State. A volunteer thinks that she saw one in the area, so Alex will spend some time there to try and get concrete evidence of the animal's presence. After Alex arrives, the body of a Forest Service employee is found in the center of the closest town, and Alex learns of an older woman who went missing in the area over a year ago. The authorities ask Alex to keep a look out for any of the woman's possessions that Alex might come across as she does her work in the wilderness. In addition, there have also been tensions between environmentalists and loggers that Alex finds herself in the middle of. It's no surprise that, soon, Alex's own life is in danger. In this third book in the Alex Carter series, Henderson immerses the reader in the flora and fauna in the area while also continuing the story of the very likable Alex.