This publication describes a rangeland simulation model which was developed to provide information relative to management and research. It provides a narrative description of the model's five basic components — 1) climate; 2) hydrology; 3) plant; 4) animal; and 5) economic — and their interfaces. An option for evaluating the impact of grasshoppers and their control is included. Input data requirements and model outputs are described. Application of the model to problems of resource management and research planning and administration is discussed. Model documentation and user guides are not included but will appear in subsequent publications.