Death Valley is a national park in California known as the hottest place in the world. These demanding conditions are caused by climatic and geographical factors. Death Valley lies between several mountain ranges, e.g., Sierra Nevada, which block clouds and humid air coming from the Pacific Ocean. When this air rises over the mountains, the moisture precipitates and falls as rain long before it reaches the valley. Only dry air reaches the lower parts of the valley. Death Valley is also the lowest place in North America -282 feet (- 86 meters) below sea level. However, its biggest mystery is not the weather but the dried lake Racetrack Playa. It is in this flat desert area that there are wandering stones that seemingly move by themselves without any apparent cause.