The Mary's Peak site was established in 2006. It is located on top of Mary's Peak, the highest mountain in the Oregon coast range. The sampling inlet is 10 m up on the tower, and gas analysis is performed with a Picarro G2302 Cavity Ringdown Spectrometer. The tower is also equipped with a set of meteorological instruments, including a radiation sensor and a heated anemometer with vane specifically developed for the harsh mountain conditions in winter. Due to its exposed position the tower measures background CO2 values of incoming air from the Pacific during stable conditions with westerly wind directions.