Gomphidius oregonensis, commonly known as Insidious Gomphidius is a mushroom found only in western North America, most commonly on the Pacific Coast. G. oregonensis can be distinguished by its spores which are the shortest in the genus, typically less than 14 µm long. Earlier in growth, G. oregonensis can be difficult to distinguish from other members of the genus Gomphidius, such as G. glutinosus which is the most common and widespread species. With age, the fruiting body becomes murky and rather insidious in appearance, hence its common name.