[6] The Elderberry longhorn beetle, California giant garter snake, and the Swainson's hawk are three threatened or endangered species that have been found living on the preserve.

Around 1770, a small group consisting of Spanish explorers decided that the Cosumnes River Preserve and other places within the Central Valley was a perfect pasture for grazing animals.

The Mexican government started issuing land grants in 1844 and John Sutter who was a European immigrant was one of the first to colonize the Cosumnes River area.

Shortly after, the Miwok moved out of the region where the Cosumnes River Preserve is and in 1999, the last person to speak Plains Miwuk died.

[6] Currently, the preserve is more than 46,000 acres (190 km2) with educational and scientific studies being conducted in one of the largest conservation efforts begun on a watershed-sized scale.

The Cosumnes River has no major dams on its course of 80 miles (130 km) and floods after heavy rains bringing in sediments that provide nutrients for the vegetation, as well as recharging groundwater levels.

In addition, removal of the man-made levees allows more inundation of floodwaters and is what ecologist Rich Reiner terms "natural process restoration".

Especially mule deer and western gray squirrel, who rely so much on the acorn crop that a poorly producing year can limit their populations.

The non-native grasses are more aggressive and produce more seed than the native perennials, which attracts seed-eaters like Botta's Pocket Gopher that also feed on acorns and oak seedlings.

[12] Restoration includes breaching the levees, allowing floodwaters to scour out the non-native grasses, reduce rodent populations and deposit sediment.

[13] The vegetation of oak, willow, alder, elderberry, cattails, and many other plants provide food, shelter and nesting sites for a wide range of wildlife, including migrating birds on the Pacific Flyway.

With increased agricultural production however, much of the groundwater underneath the Cosumnes River Preserve has been depleted so it cannot recharge the wetland habitat during the early summer.

[10] During the wet season, which occurs between late fall and early spring, much of the Cosumnes Preserve floods which provides a perfect wetland habitat for many riparian species of flora and fauna.

During the late summer and early fall, the Cosumnes River Preserve has no water flow which could potentially impact local aquatic plant species as well as fish.

Some of the species that are located close to the water are Cottonwood (Populus fremontii), cattail (Typhaceae typha), Broadleaf Arrowhead (Sagittaria latifolia), and Pampas Grass (Cortaderia selloana).

Two greatly invasive plant species that occur around the Cosumnes River Preserve are the Perennial Pepperweed (Lepidium latifolium) and Common water hyacinth (Eichhornia crassipes).

Many smaller mammal species also exist within the preserve such as muskrats (Ondatra zibethicus), black-tailed jackrabbits (Lepus californicus), and raccoons (Procyon lotor).

Two of the native fish species that have been recorded within the preserve are Chinook salmon (Oncorhynchus tshawytscha) and Tule perch (Hysterocarpus traskii).

"The scene is reminiscent of Bogart and Hepburn on the African Queen", writes author Charlie Pike in his book, Paddling Northern California.