Pinyon-juniper woodland and short and mixed-grass prairies occupy park uplands. The pinyon-juniper woodland community occurs on rocky outcrops and slopes over one-third of the park. Pinyon pine, one-seed juniper, Rocky Mountain juniper, and scrubland species such as Gambel oak, mountain mahogany and serviceberry occupy the park.

Mixed-grass prairie is made of western wheatgrass, needle and thread grass, and Indian ricegrass. Shortgrass prairie is made of blue grama, galleta and side oats grama. Saline bottomland scrubland, made of rabbitbrush, four-wing saltbush and alkali sacaton, grows in areas disturbed in the past by ground work and earthmoving activities.

Diverse wetland, riparian and aquatic plant communities have become established around the reservoir, in the Purgatoire River Valley above the reservoir and below the dam. Riparian scrubland is made of sandbar willow and typically grows adjacent to cottonwood forests.