In my time exposure, taken after sunset, the full moon rose, bathing light onto the calm surface of western Montana's Flathead Lake. Fifteen thousand years ago, this lake was the terminus of a thousand-mile-long ice flow originating in the Canadian Yukon, an arm of the vast Cordilleran Ice Sheet that covered much of what is now the northwestern United States and southwestern Canada.

Its enormous glacier carved the valley that now contains Flathead Lake and scraped rocky debris from the surrounding mountains to form its terminal moraine. The glacier slowly receded as the ice sheet melted, and the embankment that remained dammed the lake and created the largest freshwater body in the West. Measuring 30 miles long and 15 miles wide, the lake's shoreline is rimmed with glacially deposited stones and boulders tumbled and smoothed by their long journey in the ice flow.

Originally named Salish Lake after the people who had long occupied this land, its current name resulted from a misunderstanding that these Salish people practiced "head flattening." Nevertheless, the name persists, and today, the lake is partially included in and bordered by the Confederated Salish and Kootenai Tribes of the Flathead Reservation. For me, it is one of the most beautiful locations in the West: a natural lake in a rural setting encircled by the Rocky Mountains.