modified the boundaries between the park and the missile range. The missile range borders the park on all sides, with a cooperative use area designated in the park's western portion where public access is only allowed by permit. The cooperative use area includes most of the Alkali Flat region in the park's northwestern quadrant, as well as Lake Lucero and dome dunes in the southwestern quadrant. The San Andres Mountains rise beyond the park's western boundary, while Holloman Air Force Base is a short distance to the east. A rock formation called the Twin Buttes is located to the south on land administered by the Bureau of Land Management. Climate According to the Köppen climate classification system, White Sands National Park has a continental or cold semi-arid climate (BSk), bordering closely on a cold desert climate (BWk). Daily means resemble those of a humid subtropical climate (Cfa), though its relatively high elevation and low precipitation causes a higher diurnal temperature variation and shorter growing season than would be typical of such a climate. The growing season generally lasts less than six months, from April 27 to October 19 on average. The warmest months are April through October when the average high temperature reaches or exceeds and the daily mean temperature is in the range . Afternoon temperatures in June and July average around . The highest recorded temperature is , set on June 22, 1981. The cooler months are November through March when the average low temperature is below and the daily mean temperature is in the range , with December and January being the coldest months. The lowest recorded temperature is , set on January 11, 1962. The average annual precipitation is with the wettest month being August at . July through October have the most rainy days, averaging four to seven days per month. The remaining months have an average of two or three days with precipitation. Snow may occur from November through March, with an average accumulation of . Geology During the Permian Period, shallow seas covered the area that today forms White Sands National Park. The seas left behind gypsum (calcium sulfate), and subsequent tectonic activity lifted areas of the gypsum-rich seabed to form part of the San Andres and Sacramento Mountains. Over time, rain dissolved the water-soluble gypsum in the mountains, and rivers carried it to the Tularosa Basin, which has no outlet to the