Calf Island, also known as Apthorps Island, is a windswept island situated some 9 miles (14 km) offshore of downtown Boston in the Boston Harbor Islands National Recreation Area. The island has a permanent size of 18 acres (73,000 m²), plus an intertidal zone of a further 16 acres (65,000 m²), and has a thin layer of soil that supports vegetation including wild cherry, beach plum, grasses, chives, and mock orange.