of precipitation, the Black Hills ecology differs significantly from that of the plains. The mountains are thickly blanketed by various types of pines, including ponderosa and lodgepole pines, as well as spruces. Black Hills mammals include deer, elk (wapiti), bighorn sheep, mountain goats, pine marten, and mountain lions, while the streams and lakes contain several species of trout. Climate South Dakota has a continental climate with four distinct seasons, ranging from cold, dry winters to warm and semi-humid summers. During the summers, the state's average high temperature is often close to , although it cools to near at night. It is not unusual for South Dakota to have severe hot, dry spells in the summer with the temperature climbing above several times a year. Winters are cold with January high temperatures averaging below freezing and low temperatures averaging below in most of the state. The highest recorded temperature is at Usta on July 15, 2006 and the lowest recorded temperature is at McIntosh on February 17, 1936. Average annual precipitation in South Dakota ranges from semi-arid conditions in the northwestern part of the state (around ) to semi-humid around the southeast portion of the state (around ), although a small area centered on Lead in the Black Hills has the highest precipitation at nearly per year. South Dakota summers bring frequent, sometimes severe, thunderstorms with high winds, thunder, and hail. The state's eastern part is often considered part of Tornado Alley, and South Dakota experiences an average of 30 tornadoes each year. Severe blizzards and ice storms often occur during winter. National parks and monuments South Dakota has several sites administered by the National Park Service. Two national parks have been established in the state, both in its southwestern region. Wind Cave National Park, established in 1903 in the Black Hills, has an extensive cave network and is home to a large herd of bison. Badlands National Park was established in 1978, and features an eroded, brightly colored landscape surrounded by semi-arid grasslands. Mount Rushmore National Memorial in the Black Hills was established in 1925. The sculpture of four U.S. Presidents was carved into the mountainside by sculptor Gutzon Borglum. Other areas managed by the National Park Service include Jewel Cave National Monument near Custer, the Lewis and Clark National Historic Trail, the Minuteman Missile National Historic Site, which features a decommissioned nuclear missile silo and a separate missile control