Caswell Memorial State Park, Nature reserve in Stanislaus County, United States.

Caswell Memorial State Park is a nature reserve on the banks of the Stanislaus River in California's San Joaquin Valley. The land is made up of riparian woodland with old valley oaks, open grassland, and stretches of riverbank that run along the southern edge of the park.

The land was originally owned by Thomas Caswell, and his descendants donated part of it to the California state park system in the 1950s. The park has grown since then, but the original donated land remains the core of what visitors explore today.

The park takes its name from Thomas Caswell, on whose land it was created; his children and grandchildren donated 134 acres to California in the 1950s. The riparian oak woodland it protects is a threatened habitat type that once flourished across the Central Valley. The endangered riparian brush rabbit lives here, reduced to a few hundred individuals.

The park has a campground with restrooms and showers, making it possible to stay overnight. Trails are easy to follow and mostly flat, running close to the river, so no special gear is needed for a visit.

The park is one of the last places on earth where the riparian brush rabbit survives, a small animal that depends entirely on a very specific type of riverside vegetation. Researchers have run active recovery programs here because the species cannot exist outside this kind of habitat.