In North America, mammoth (Mammuthus) fossils are key to biostratigraphic indicators for the Irvingtonian and Rancholabrean land mammal ages that can provide information regarding Pleistocene environmental patters and processes. They occur in a variety of geologic contexts in the western Snake River Plain (WSRP), southwestern Idaho. This paper provides a review of previously known localities and a preliminary assessment of the geology of mammoth fossils recently recovered northeast of Nyssa, Oregon.