Thermally-driven wind systems in mountainous areas cover a wide range of scales and phenomenons.  Air Quality can be the largest problem concerning the human population when high concentrations of pollutants are kept in the boundary-layer due to stagnant conditions associated with cold air pooling and transport by local wind systems. This paper describes a field experiment that took place during 14-17 March 1998 in which the wind system of a  vertical sidewalled valley was investigated. This Valley is the Yosemite Valley in California. The physical parameters of the local wind system in Yosemite Valley as well as the Sierra Nevada on a whole are unknown, and with the increased usage in this National Park and additionally the increase in pollution levels of California's Central Valley this field experiment deems value and gained importance. Further, the knowledge of the mountain-valley wind system for the Sierra Nevada is not well understood. There are complex interactions of the local circulations with the larger scale synoptic flows which can have a significant effect on pollution transport into the pristine alpine environment.