The purpose of this dissertation is to examine long term changes in the overnight backcountry hiker population at Grand Canyon National Park (GCNP) between 1984 and 2004. Longitudinal studies of visitor behavior in wildland recreation settings have been relatively rare but offer great potential for the improvement of management, clarification of conceptual problems and the generation of new research questions previously unconsidered in the outdoor recreation literature. This study aggregates data from two representative surveys of overnight backcountry hiking permit holders at GCNP. The first the first survey was conducted in 1984 and the second was conducted in 2004. This study explores how the population has changed in terms of hiker characteristics, the characteristics of their visits, and the experiences achieved on hiker visits. To assess the effect of changes in hikers' characteristics on the characteristics of their visits, and the experience outcomes of their visits, the data were analyzed using an Age-Period-Cohort (APC) framework. In the APC framework, longitudinal change is a function of three causal forces: differences in the life-course positions of visitors, differences in the historical circumstances of the research, and differences in the preferences and characteristics of the cohorts that make up the populations. The results indicate that visitors in 2004 were older, more experienced hikers and were more likely to hike with family members than other group types than were hikers in 1984. There was remarkable stability in the outcomes sought by hikers, although the relative importance of family related outcomes increased modestly. APC analysis suggested that differences in social groups and experience outcome importance between hikers in 1984 and 2004 are related to the age differences of the hiker populations. This study broadens the understanding of visitor populations, has implications for management and researchers, reaffirms that just as with ecological systems, visitor populations are dynamic and that monitoring the social systems within wildland recreation areas is important for the maintenance and improvement of the quality of visitor experiences. [The dissertation citations contained here are published with the permission of ProQuest LLC. Further reproduction is prohibited without permission. Copies of dissertations may be obtained by Telephone (800) 1-800-521-0600. Web page: http://www.proquest.com/en-US/products/dissertations/individuals.shtml.]