Lists of dominant plants in the prehistoric ecology and plant community of the Waterman Mountains area in the monument have been published in a sequence that currently dates back to the last glacial period, the Late Wisconsin glatial period. Dominant trees of that era, based upon pollen records, were Utah juniper (Juniperus osteosperma), single-leaf pinyon (Pinus monophylla), and redberry juniper (Juniperus pinchotii), and understory plants included Monardella arizonica.