The Utukok River on Alaska’s North Slope starts off in the Brooks Range and travels towards the Arctic Ocean, passing through what is considered part of the Naval Petroleum Reserve on the way. The river cuts through a huge package of sedimentary rocks that were deposited in the Cretaceous and Tertiary periods.
The Brooks Range was assembled from chunks of continental rocks that rode along a subducting oceanic plate and eventually slammed into the North American continental margin starting during the Cretaceous – much of Alaska today is actually formed from these chunks of accreted rock. As these chunks of continent collided, they caused the uplift of the mountains. Erosion of these mountains sent sediments into basins to the north – that’s where today the oil reserves are located. These wavy patterns are ripples found in a sandstone chunk sticking up along the rivers edge – a remnant of sediments being carried by an ancient predecessor of the modern river.