1. Hendee, J. C. et al. 1968. Wilderness users in the Pacific Northwest—their characteristics, values, and management preferences. Portland, Oregon: Pacific Northwest Forest and Range Experiment Station, USDA Forest Service Research Paper. DNW-61.
2. Shelby, B. B. 1976. “Social Psychological Effects of Crowding in Wilderness: The Case of River Trips in the Grand Canyon.” Ph.D. Dissertation, Department of Sociology, University of Colorado, Boulder, Colorado.