Boyce Thompson Arboretum is the oldest and largest botanical garden in the state of Arizona. It is one of the oldest botanical institutions west of the Mississippi River. Founded in 1924 as a desert plant research facility and “living museum”, the arboretum is located in the Sonoran Desert on 392 acres (159 ha) along Queen Creek and beneath the towering volcanic remnant, Picketpost Mountain. Boyce Thompson Arboretum is on U.S. Highway 60, an hour's drive east from Phoenix and 3 miles (4.8 km) west of Superior, Arizona.