Wimmer Grasslands is part of the Winters Oxbow about two miles east of Putah Diversion Dam on the south bank. It was a gravel pit in the 1960s, then became a solid thicket of Himalayan blackberries until 2004 when a grant from the Wildlife Conservation Board provided funds for weed control and native grass restoration. The site is now covered with creeping wild rye, a native grass that has excluded most weeds.