One of the oldest archaeological sites in the Americas has been discovered in western Idaho, according to a study published today in the journal Science.

Radiocarbon dates show that people were creating tools and butchering animals in Cooper’s Ferry between 15,000 and 16,000 years ago, making Cooper’s Ferry a rare and important addition to the handful of archaeological sites that are upending the traditional theory of the peopling of the Americas.

Until a couple decades ago, Clovis stone tools, which are generally about 13,000 years old, were considered to be the first human technology in the Americas. As part of the “Clovis-first” hypothesis, most researchers believed that the people who made these tools first entered North America on foot from