The modern history of the Mojave Desert is intertwined with the histor y of humans along Route 66. In this land of extremes, temperatures can reach 120 degrees in the summer and dip below freezing in the winter. Rich in natural and human history, this is home to the newest and lar gest desert preserve in the United States: The Mojave National Preserv e. This diverse preserve has Joshua tree forests, sand dunes, creosote flats, lava fields, salt-encrusted playas and caves. Learn about the discovery of Mitchell Caverns and venture underground to examine some of the unique formations of this marvelous cavern. Then explore volcan ic fields and observe how plants cling to life in the middle of hot, b arren lava flows.