San Luis Lakes State Park features an 890 surface-acre playa lake, with water levels stabilized as in a reservoir, amid rolling sandhills and alkaline flats of San Luis Valley. The park is covered by Recent parabolic deflation dunes overlying Pliocene and Pleistocene outwash fan deposits. Pleistocene glaciation represents the last major geologic event; outwash from melting glaciers was deposited across the valley floor and many large playas were created. The park occupies a rift valley that escaped the Tertiary uplifts of the Sangre de Cristo Mountains; the valley created by both rift faulting and a graben which sank as the mountains rose. Ecologically, park uplands are dominated by saline bottom land shrublands, cold desert shrublands and salt meadows. Common plant species for the area include greasewood, rubber and Greene rabbitbrush, four-wing saltbush, yucca, western wheatgrass, alkali cordgrass, saltgrass, Indian ricegrass, needle-and-thread grass, sandhills muhly and blue grama. Diverse wetland and aquatic plant communities have become established around and in the playa including habitat for the rare slender spider-flower.

Many species of migratory and resident birds are known for this area and the park is an important breeding and resting habitat for waterfowl and shorebirds. American avocet, white pelican, western grebe, ducks, geese, long-billed curlew, black-crowned night heron and western sandpiper are commonly observed. Pronghorn antelope and elk are often seen, as are cottontail rabbit, jackrabbit, coyote and least chipmunk. Two endemic mammal subspecies of special concern in the park are the northern pocket gopher and the silky pocket mouse. Many anglers are attracted by fishing opportunities for the cold-water rainbow trout.