This document discusses using a mass balance model to simulate water levels at Mono Lake, which is located in California. The model will be constructed by students in a geology course to introduce them to modeling environmental issues. The document provides context on the course and assignment. It describes the history of declining lake levels due to Los Angeles diverting water from the Mono Lake basin. It outlines the steps to construct a water balance model for Mono Lake using a stock and flow diagram and equations. The model will be calibrated using historical data and used to predict future lake levels under different scenarios.