The lone leaf and two of the samara's were found in an outcrop of shale on Knob Hill north of Republic, Washington identified as Burke Museum of Natural History and Culture location UWBM B2737.

Each of the sites are considered outcroppings of early Eocene, Ypresian,[2] shale belonging to the Klondike Mountain Formation.

[1] The Klondike Mountain Formation, along with site of the same age in British Columbia preserve upland temperate floras which were first interpreted as being Microthermal,[1] however further study has shown them to be more mesothermal in nature.

[2] The plant community preserved in the Klondike Mountain formation is a mixed conifer-broad leaf forest with large pollen elements of birch and golden larch, but also having notable traces of fir, spruce, cypress, and palm.

Wolfe and Tanai published their 1987 type description for A. toradense in the Journal of the Faculty of Science, Hokkaido University.