The Similkameen � Chopaka Unit, which encompasses 1,139 acres, is located 18 miles west of Oroville along the Chopaka road. Lands to the north and south of the unit are privately owned and used primarily for hay production and cattle grazing. To the west are the steep slopes of Chopaka Mountain, which is owned by the Bureau of Land Management, rising to elevations of 8,000 feet on Hurley Peak. This slope provides a scenic backdrop to the lush valley bottom that is the Similkameen - Chopaka Wildlife Unit. The Similkameen River forms the eastern boundary and is lined with cottonwoods, aspen and alder. Deciduous shrubs include hawthorn, willows, dogwood, rose and snowberry, and grasses are dominated by introduced species like smooth brome. The center of the area has historically been farmed and is presently in a grass/alfalfa hay field of approximately 350 acres. To the west and across the Chopaka road is native shrub-steppe with sagebrush, rabbitbrush, and bitterbrush with grasses including bluebunch wheatgrass, Idaho fescue, and wild rye. An invasive plant species, diffuse knapweed, has severely infested this area, though efforts have been made to combat the problem knapweed. Stands of conifers in this area include ponderosa pine, and Douglas fir.