Crater Lake National Park: The Mountain That Collapsed Into a Lake, Crater Lake National Park was formed after the collapse of Mount Mazama nearly 8,000 years ago. With no rivers flowing into it, the lake is filled almost entirely by snow and rain, filtered through volcanic rock, creating one of the deepest and clearest lakes on Earth. #nationalpark #hiddenhistory #parkhistory #americanhistory #craterlake national park history, hidden history, American history, documented stories, public lands,