Blue Lake Crater, or Blue Lake Maar, is a little-known Holocene volcanic crater in Oregon’s Metolius River basin, formed as three overlapping maars now occupied by Blue Lake. It erupted sometime within the past 4,000 years, though estimates range from about 3,440 to roughly 1,330 years ago. The crater is linked to nearby vents and spatter cones, and its rim preserves welded volcanic fragments and large bombs, with a collapsed northern side and intact southern wall. The deep, vividly colored lake and its unusual chemistry have drawn scientific interest, while the surrounding forested basin supports diverse wildlife and remains protected from large-scale development.