In November, EPA’s Clean Air Status and Trends Network (CASTNET) established its seventh tribal air monitoring site in partnership with the Confederated Tribes of the Umatilla Indian Reservation (CTUIR) and Region 10. Prior to CASTNET, the CTUIR Air Quality Division conducted continuous PM2.5 monitoring. More recently, they identified CASTNET as a way to expand their air quality monitoring. The small-footprint site located near Dayton, WA, measures ambient concentrations of O3, SO2, total NO3, SO4, NH4 and NH3. CASTNET has partnered with tribes since 2002, and these partnerships build air monitoring capacity on tribal lands while filling spatial gaps in the network. Network basics, funding mechanisms, tribal site details, and measurement data will be described.