Understanding the impacts of human recreation on natural resources is of critical importance in constructing effective management strategies. The Grand Canyon River Trip Simulator is a computer program that models complex, dynamic human-environment interactions in the river corridor of the Grand Canyon National Park. The system consists of a database and simulator engine. The database contains 487 trip diaries that report all stops for activities and camping along the 447 kilometer Colorado River corridor within the purview of the National Park Service. The computer simulation employs statistics and artificial intelligence in creating an individual-based modeling system. This simulation system successfully models the recreational rafting behavior and captures the decision making of rafting parties as they responsively seek to optimize their experience. The model allows the Park managers to assess the likely impact of various alternative management scenarios for rafting trips on the Colorado River. The Grand Canyon River Trip Simulator advances our abilities to model complex systems in the context of human-environment interactions. It may serve as a suitable template for modeling a suite of other complex adaptive systems including ecosystems.