Curly Creek Falls is an 86-foot waterfall in southwestern Washington near Swift Reservoir in the Lewis River region of the Mount St. Helens National Volcanic Monument. Curly Creek drops through a wooded gorge before joining the Lewis River, and the falls are especially notable for two natural basalt arches at the brink, remnants of an old lava flow. Seasonal water levels change the scene: spring high water can partly hide the first arch, while later in the year low flow can expose a hollow cavity in the upstream bedrock. Mossy rocks, old-growth Douglas fir, and hemlock surround the site, which is also known as Curly or Miller Falls.