Horse Rock Ridge Research Natural Area (HRR RNA) was established in June 1995 to protect the best remaining example of a grassy "bald" (treeless area) on the western margin of the Cascade Range and its associated botanical, wildlife, and scenic values. This bald is surrounded by old-growth Pseudotsuga menziesii/Tsuga heterophylla (Douglas-fir/western hemlock) forest in the Coburg Hills on the eastern edge of the Willamette Valley in western Oregon. The site is recognized for its considerable diversity of plant species that includes both Willamette Valley plants as well as plants more often found in the montane zone of the Cascade Range. There are also several species present at the site that are normally found east of the Cascade Range. This guidebook describes the area, environment, biota, disturbance history, research, and access.