Answer: You didn't mention whether the site is sunny or shady so I can't make a single recommendation. However, the following is a list of plants from Colorado State University:
Groundcovers and Ornamental Grasses
Antennaria rosea (Pink Pussytoes), full sun, purple blossoms early summer, short ground cover 4-12 inches, spreads rapidly.
Bouteloua curtipendula (Sideoats, Grama Grass), full sun, green with purple tips midsummer, medium meadow grass 1-2, remarkably hardy, non-invasive.
Calamagrostis acutiflora (Karl Foerster Feather Reed Grass), full sun, green with tan tips, tall meadow grass 3-6 feet.
Cerastium tomentosum (Snow-in-summer), part to full sun, white blossoms late spring, medium ground cover 8-12 inches, can be invasive
Delosperma cooperi (Pink Hardy Ice Plant), full sun, purple blossoms late spring, ground cover 6 inches, good in hot or dry conditions.
Delosperma nubigenum (Hardy Yellow Ice Plant), full, red in winter, yellow blossoms late spring, short ground cover 1-3 inches.
Festuca ovina glauca (Blue Fescue), light shade, short meadow grass 12 inches.
Helictotrichon sempervirens (Blue Avena Grass), light shade, meadow grass 2-4 feet. Miscanthus sinensis (Miscanthus Grass), light shade, tan in winter, tall meadow grass 4-10 feet.
Oryzopsis hymenoides (Indian Ricegrass), tan in winter, short meadow grass 1-2 feet.
Pennisetum alopecuroides (Fountain Grass), full sun, tan in winter, medium meadow grass 2-3 feet.
Pennisetum setaceum (rubrum) Purple Fountain Grass, full sun, medium meadow grass 2-4 feet.
Santolina chamaecyparissus (Lavender Cotton), full sun, yellow blossoms midsummer, tall ground cover 12-18 inches.
Polygonum affine (Himalayan Fleeceflower), light shade, red in fall, purple blossoms late summer, medium ground cover 6-10 inches, tends to choke out weeds.
Sedum spectabile (Showy Stonecrop), light shade, red blossoms in fall, flowery plants 18-24 inches.
Sempervivum (Hens and Chicks), light shade, short spiky ground cover 2-4 inches.
Thymus pseudolanuginosus (Woolly Thyme), full sun or dry shade, short ground cover 1-2 inches.
Veronica pectinata (Blue Woolly Speedwell), sun or part shade, blue blossoms midspring, short ground cover 1-2 inches.
Zinnia grandiflora (Rocky Mountain Zinnia), full sun.
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