A wave-carved stone arch survives high and dry in the Nevada desert

Toward the end of the last Ice Age, roughly 17,500 years ago, a massive body of water known as Lake Bonneville covered much of western Utah and spread into neighboring parts of Nevada and Idaho. At its peak, around 5,100 feet above sea level, the lake carved what geologists call the Bonneville Shoreline before spilling over Red Rock Pass in what is now Idaho, unleashing a huge flood that surged down the Snake River and eventually reached the Pacific Ocean via the Columbia River.

As the escaping water cut deeper into the landscape, the lake's surface fell by more than 400 feet until the erosion hit a layer of tough bedrock that halted further downcutting. This pause allowed a new shoreline, called the Provo Shoreline, to form at the lower elevation. Researchers believe a river continued flowing out through this channel into the Snake for roughly a thousand years before a drying climate pushed the lake's level below the outlet altogether.

Traces of an inland sea

A lake of that size and depth was capable of carving coastal features usually associated with oceans rather than lakes. Window Rock is one such feature: a large arch cut by wave action, now perched high on a dry desert ridge. Sitting at roughly 4,839 feet in elevation, the arch was likely formed before the lake's surface dropped to the level of the Provo Shoreline.

Today, reaching Window Rock means navigating a series of unpaved roads that demand a high-clearance vehicle, with four-wheel drive recommended for the final stretch. The route begins near Interstate 80's Exit 398 and winds through desert terrain before ending in a short, manageable hike to the arch itself.