Further collecting in outcrops of Passamari Formation in the Ruby River Basin of southwestern Montana lead to the description of another species, Eucommia brownii by Herman F. Becker in 1960.

The slightly younger Coldwater Beds outcropping near Quilchena, British Columbia where the species is associated with the leaf morphospecies Eucommia rolandii are the northern most.

Fossils recovered from the Ypresian Green River Formation outcrops near Rainbow, Utah, Wardell Ranch and Douglas Pass, Colorado extended the geographic range to the south.

All the fossils studied from Washington, British Columbia, Oregon, Colorado, and Utah fall into the range of variation seen in specimens from the Renova Formation.

The Clarno formation specimens show a slightly lower average length to width ratio, but were still assigned to E. montana.