The Granite Mountain Atmospheric Sciences Testbed (GMAST) facility is located at the U.S. Army Dugway Proving Ground (DPG) and represents a network of various meteorological sensors placed at and around Granite Mountain and other mountains at DPG. A core infrastructure of weather sensors has been developed including instrumented towers and remote sensors, along with automated data collection and archival systems. The goal is to obtain long term data on airflow patterns and thermal conditions produced by interaction of large scale flows with complex terrain, thermally induced circulations, and other complex terrain meteorological phenomena. The DPG mission is to conduct tests and assessments of biological and chemical weapon systems, and GMAST data will help Meteorology Division provide weather related support during these efforts. This is also an ideal setting for researchers in the area of complex terrain flows and dispersion to organize more specialized studies using their own equipment. The DPG Meteorology Division will be able to provide long-term meteorological data before and during the test in order to better plan and conduct field projects. Also, the reliable and detailed weather forecasts obtained using the Four-Dimensional Weather (4DWX) modeling system will be a valuable tool for scheduling and planning of specific Intensive Observational Periods (IOPs). The intent is that this large data set in combination with visitors' specialized datasets will contribute to advancement of our understanding of flow, turbulence and dispersion in complex terrain and help improve modeling capabilities and numerical model evaluations. The first field study that will utilize the GMAST facility is the MATERHORN (MountAin TERrain atmospHeric mOdeling and obseRvatioNs) project where two field experiments are planned for Spring and Fall of 2012. This is a collaboration of a large number of universities and other institutions, and the GMAST facility will play an important role in the field testing of the project. This presentation will give a detailed overview of the facility, both terrain characteristics and instrumentation network, and a short description of the MATERHORN project goals and field test plans.