The Sunnyside Headquarters unit covers 2,786 acres one mile north of Mabton and five miles south of Sunnyside. The Headquarters unit is a collection of small agricultural fields, interspersed with diverse habitats. Six ponds or lakes vary in size from 15 to 100 surface acres and evidence of old river oxbows can also be found throughout. Vegetation ranges from wetland species to upland perennial grasses and forbs to mature riparian woodlands. Russian olives have been invading for several years. Horseshoe Lake, an old river oxbow, is an important resting place for wintering waterfowl. Horseshoe Lake falls within the Snipes Reserve, which is closed to all public entry. The largest lake, 100-acre Giffen Lake, is invaded by white lily pads. Farming has been reduced in recent years by restoring some of the dryland fields to native grasses and shrubs. About 468 acres remain under an agricultural lease, with about 124 acres in a dry land alfalfa/small grain rotation and the remainder irrigated. Waterfowl and upland game bird hunting and fishing are most popular.