The Cosumnes River is the last undammed river flowing from the Sierra Nevada mountain range into the Great Central Valley.
Originating at an elevation of 7,600 feet, the headwaters of the Cosumnes River flow through the Eldorado National Forest and support native trout fisheries and many other aquatic-dependent species. Descending towards the Central Valley, the river passes through blue oak, grassland and vernal pool communities. The lower reaches of the river also provide critical salmon spawning habitat.
The Conservancy's Cosumnes River Preserve on the lower floodplain of the river harbors valley oak riparian forest and freshwater wetlands used by thousands of wintering migratory birds.
The Nature Conservancy, in partnership with local landowners, businesses, other private partners and state and local government agencies, is pursuing approaches to conservation that will safeguard critical ecological processes within the 1,200-square-mile watershed to maintain the biological and hydrological health of this important natural system.
The Cosumnes River Preserve
SIZE: 5,200 acres
LOCATION: Sacramento County, on the eastern edge of the Sacramento-San Joaquin delta; between California Highway 99 and Interstate 5. The nearest towns are Walnut Grove and Gait.
HISTORY: The Miwok Indians once lived in the area, hunting, fishing for salmon and collecting acorns for a living. In later years settlers cleared much of the land for farming and cattle grazing, presently the predominant uses of the land surrounding the preserve.
GEOGRAPHY: Although nearly 100 miles from the ocean, the lower reaches of the Cosumnes River are affected by ocean tides funneling into the delta through San Francisco Bay, pushing fresh water back up the Cosumnes. The average elevation is less than ten feet. The climate is Mediterranean, with hot, dry summers and cool, moist winters. Tule fogs are common in mid-winter. Because there are no major dams on the Cosumnes, frequent flooding
occurs in response to heavy winter rains. The load of rich silt carried by flood water introduces valuable nutrients to adjacent wetlands and grasslands. Because of its historic stands of valley oak, portions of the preserve have been selected as a National Natural Landmark.
FLORA: The Cosumnes River Preserve protects two plant communities now rare: riparian (stream-side) forest and freshwater marsh; less than 4% of each community remains intact in the state. The preserve supports the finest remaining example of valley oak riparian forest. Valley oak (Quercus lobata), and Fremont cottonwood (Populus fremontii) form the forest's tall, continuous canopy. The luxuriant forest growth is due to the abundance of available water during the optimum growing temperatures of summer. Great vines of wild grape (Vitus californica) festoon the trees, giving the forest an appearance that John Muir described as "tropical luxuriance." Freshwater marshes bordering the forest support vigorous growth of tules (Scirpus) and cattails (Typha). Annual grasslands and cultivated fields occur in drier parts of the preserve.
FAUNA: The river itself harbors runs of salmon and steelhead. River otter, beaver and muskrat also occupy the water. The bordering riparian forest is home to raccoon, black-tailed mule deer, mink and many song birds. The rare giant garter snake is present and the Pacific tree frog is common. More than 200 species of birds have been recorded on and around the preserve, including several nesting pairs of endangered Swainson's hawks. In winter, the marshes support impressive numbers of greater and lesser sandhill cranes, Ross's white-fronted and Canada geese, tundra swans and numerous species of ducks. Resident birds such as great blue herons, black-crowned night herons and black-shouldered kites are common.
MANAGEMENT: The Cosumnes River Preserve is jointly owned by The Nature Conservancy, The Bureau of Land Management, Ducks Unlimited, the California Department of Fish and Game, and the Sacramento County Department of Parks and Recreation. Each partner organization contributes to management of the preserve. The Conservancy is restoring the riparian forests. Valley oaks, the dominant species, Oregon ash, Fremont's cottonwood, box elder, willows, wild rose and elderberry are being planted to mimic the mixture of trees and shrubs found in the riparian forest.
Through wetland enhancement work by Ducks Unlimited and the Bureau of Land Management, the wetlands are being managed to create diverse aquatic plant communities. These provide nesting and brood-rearing habitats for waterfowl during spring and summer. Fall and winter flooding provides resting and feeding areas for migrating and wintering birds.
VISITOR HINTS: Please remember:
1. Hunting, fishing, biking and collecting are prohibited on the preserve.
2. No fires, camping, or smoking.
3. Pets, firearms and radios are prohibited.
4. Mosquito repellent is necessary during the summer.
ACCESS: Take Interstate 5 to Twin Cities Road exit, about midway between Stockton and Sacramento. Take Twin Cities Road east to Franklin Boulevard. Travel south on Franklin Boulevard. The Willow Slough trail head is located on your left 0.2 mile past Desmond Road; it is the start of a 3-mile nature trail, open every day during daylight hours. The Visitor Center is 0.4 miles from the trail head, on your left. It houses interpretive panels describing the natural history of the preserve and restoration activities.
Membership in The Nature Conservancy, an international, private nonprofit conservation organization, begins at $25. Send membership contributions or inquiries to:
The Nature Conservancy
201 Mission Street, 4th Floor
San Francisco, CA 94105
The preserve address and information line are:
Cosumnes River Preserve
13501 Franklin Boulevard
Galt, CA 95632
Ducks Unlimited is also a membership organization.
Send inquiries to:
Ducks Unlimited, Inc.
3074 Gold Canal Drive
Rancho Cordova, CA 95670