Niagara Falls Rainbow

This panorama looks across the Niagara River toward the two largest of the three waterfalls that make up Niagara Falls: the American Falls on the near side and the curving Horseshoe Falls (also called the Canadian Falls) beyond it. A double rainbow, formed by sunlight refracting through the rising mist, arcs over the gorge connecting both sides of the river, which marks the border between Ontario, Canada, and New York, USA.

The falls were carved by the Niagara River as it drains Lake Erie into Lake Ontario, cutting back through layers of dolostone and shale left exposed after the retreat of glacial ice at the end of the last ice age. The constant erosion of the softer rock beneath the harder caprock has slowly moved the brink of the falls upstream over thousands of years, a process still measurable today. Horseshoe Falls carries the great majority of the river's flow, which is why its mist plume towers far higher than the American Falls beside it.

Niagara Falls has drawn travelers since the early 19th century, when it became one of the first popular tourist destinations in North America and, later, a well-known honeymoon spot. In this puzzle, the long horizontal sweep of the falls and the pale arc of the rainbow give clear, high-contrast lines to sort first, while the churning white water in the foreground makes a good texture-matching section to fill in once the edges are placed.