Wetland plants such as cattails and bulrush are plentiful along the Snake River. Native dry land vegetation, including big sagebrush and rabbitbrush, survives among the lava rock boulders.
Flora on the upland plateau was once a vast complex of Wyoming big sagebrush (Artemisia tridentata ver. wyomingensis) association. Some of the Monument's west boundary areas were cleared and now support common rabbitbrush (Chrysothamnus nauseosus), and introduced grasses and weeds.
Vegetation on the Monument’s bluffs is sparse in many areas due to the steepness of the slopes and low precipitation.
Greasewood (Sarcobatus vermiculatus) and rabbitbrush are the dominant shrubs where the soils are more alkaline. Scattered occurrences of four-wing saltbush (Atriplex species) occur where soils contain more calcite. Russian thistle (Salsola kali), the ubiquitous tumbleweed, predominates on disturbed sites.