Crater Lake was formed 7,700 years ago when a violent eruption triggered the collapse of a tall peak, an event witnessed by Native Americans. Fed by rain and snow, it is the deepest lake in the USA and one of the most pristine on earth. Its blue water and dramatic setting atop the Cascade Mountain Range inspire scientists, artists, photographers, and sightseers alike. Summers there are short but sunny, with July, August, and September offering the best chance for warm, dry weather, while May, June, and October alternate between sunshine, rain, and snow. Winters are long and snowy, as storms from the Pacific Ocean bring an annual average of 43 feet of snow at Park Headquarters because of the park's position at the crest of the Cascade Mountains.